diff --git a/core/includes/install.inc b/core/includes/install.inc
index f5d7399..3126c80 100644
--- a/core/includes/install.inc
+++ b/core/includes/install.inc
@@ -411,7 +411,9 @@ function drupal_install_system() {
   require_once DRUPAL_ROOT . '/' . $system_path . '/system.install';
   $system_versions = drupal_get_schema_versions('system');
   $system_version = $system_versions ? max($system_versions) : SCHEMA_INSTALLED;
-  drupal_container()
+  // Now that we have a {key_value} database table, we need a fresh container,
+  // so we can actually store schema data and configuration.
+  drupal_container(NULL, TRUE)
     ->get('keyvalue')
     ->get('system.schema')
     ->set('system', $system_version);
@@ -426,6 +428,7 @@ function drupal_install_system() {
 
   // Clear out module list and hook implementation statics.
   system_list_reset();
+  module_list_reset();
   module_implements_reset();
 
   config_install_default_config('module', 'system');
diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index f54eb73..d28316b 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -1623,9 +1623,6 @@ function theme_menu_link(array $variables) {
  */
 function theme_menu_local_task($variables) {
   $link = $variables['element']['#link'];
-  $link += array(
-    'localized_options' => array(),
-  );
   $link_text = $link['title'];
 
   if (!empty($variables['element']['#active'])) {
@@ -1872,8 +1869,8 @@ function menu_local_tasks($level = 0) {
   $data = &drupal_static(__FUNCTION__);
   $root_path = &drupal_static(__FUNCTION__ . ':root_path', '');
   $empty = array(
-    'tabs' => array(),
-    'actions' => array(),
+    'tabs' => array('count' => 0, 'output' => array()),
+    'actions' => array('count' => 0, 'output' => array()),
     'root_path' => &$root_path,
   );
 
@@ -1925,7 +1922,8 @@ function menu_local_tasks($level = 0) {
     // Tab parenting may skip levels, so the number of parts in the path may not
     // equal the depth. Thus we use the $depth counter (offset by 1000 for ksort).
     $depth = 1001;
-    $actions = array();
+    $actions['count'] = 0;
+    $actions['output'] = array();
     while (isset($children[$path])) {
       $tabs_current = array();
       $actions_current = array();
@@ -1962,7 +1960,6 @@ function menu_local_tasks($level = 0) {
               '#theme' => 'menu_local_task',
               '#link' => $link,
               '#active' => TRUE,
-              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
             $next_path = $item['path'];
             $tab_count++;
@@ -1975,7 +1972,6 @@ function menu_local_tasks($level = 0) {
               $actions_current[] = array(
                 '#theme' => 'menu_local_action',
                 '#link' => $link,
-                '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
               );
               $action_count++;
             }
@@ -1984,7 +1980,6 @@ function menu_local_tasks($level = 0) {
               $tabs_current[] = array(
                 '#theme' => 'menu_local_task',
                 '#link' => $link,
-                '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
               );
               $tab_count++;
             }
@@ -1992,8 +1987,10 @@ function menu_local_tasks($level = 0) {
         }
       }
       $path = $next_path;
-      $tabs[$depth] = $tabs_current;
-      $actions = array_merge($actions, $actions_current);
+      $tabs[$depth]['count'] = $tab_count;
+      $tabs[$depth]['output'] = $tabs_current;
+      $actions['count'] += $action_count;
+      $actions['output'] = array_merge($actions['output'], $actions_current);
       $depth++;
     }
     $data['actions'] = $actions;
@@ -2039,7 +2036,6 @@ function menu_local_tasks($level = 0) {
               '#theme' => 'menu_local_task',
               '#link' => $link,
               '#active' => TRUE,
-              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
             $next_path = $item['tab_parent'];
             if (isset($tasks[$next_path])) {
@@ -2050,14 +2046,14 @@ function menu_local_tasks($level = 0) {
             $tabs_current[] = array(
               '#theme' => 'menu_local_task',
               '#link' => $link,
-              '#weight' => isset($link['weight']) ? $link['weight'] : NULL,
             );
           }
         }
       }
       $path = $next_path;
       $parent = $next_parent;
-      $tabs[$depth] = $tabs_current;
+      $tabs[$depth]['count'] = $count;
+      $tabs[$depth]['output'] = $tabs_current;
       $depth--;
     }
     // Sort by depth.
@@ -2079,7 +2075,7 @@ function menu_local_tasks($level = 0) {
   }
   // @todo If there are no tabs, then there still can be actions; for example,
   //   when added via hook_menu_local_tasks_alter().
-  elseif (!empty($data['actions'])) {
+  elseif (!empty($data['actions']['output'])) {
     return array('actions' => $data['actions']) + $empty;
   }
   return $empty;
@@ -2192,7 +2188,7 @@ function menu_contextual_links($module, $parent_path, $args) {
 function menu_primary_local_tasks() {
   $links = menu_local_tasks(0);
   // Do not display single tabs.
-  return count($links['tabs']) > 1 ? $links['tabs'] : '';
+  return ($links['tabs']['count'] > 1 ? $links['tabs']['output'] : '');
 }
 
 /**
@@ -2201,7 +2197,7 @@ function menu_primary_local_tasks() {
 function menu_secondary_local_tasks() {
   $links = menu_local_tasks(1);
   // Do not display single tabs.
-  return count($links['tabs']) > 1 ? $links['tabs'] : '';
+  return ($links['tabs']['count'] > 1 ? $links['tabs']['output'] : '');
 }
 
 /**
@@ -2209,7 +2205,7 @@ function menu_secondary_local_tasks() {
  */
 function menu_local_actions() {
   $links = menu_local_tasks();
-  return $links['actions'];
+  return $links['actions']['output'];
 }
 
 /**
@@ -3553,6 +3549,7 @@ function _menu_router_build($callbacks) {
     $item['to_arg_functions'] = empty($to_arg_functions) ? '' : serialize($to_arg_functions);
     $item += array(
       'title' => '',
+      'weight' => 0,
       'type' => MENU_NORMAL_ITEM,
       'module' => '',
       '_number_parts' => $number_parts,
@@ -3560,9 +3557,6 @@ function _menu_router_build($callbacks) {
       '_fit' => $fit,
     );
     $item += array(
-      // Default MENU_DEFAULT_LOCAL_TASKs to a weight of -10, so they appear as
-      // first tab by default.
-      'weight' => ($item['type'] & MENU_DEFAULT_LOCAL_TASK) == MENU_DEFAULT_LOCAL_TASK ? -10 : 0,
       '_visible' => (bool) ($item['type'] & MENU_VISIBLE_IN_BREADCRUMB),
       '_tab' => (bool) ($item['type'] & MENU_IS_LOCAL_TASK),
     );
diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index 6718e87..7513cb8 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -17,6 +17,7 @@
 function _drupal_maintenance_theme() {
   global $theme, $theme_key, $conf;
 
+  require_once DRUPAL_ROOT . '/core/includes/database.inc';
   require_once DRUPAL_ROOT . '/' . variable_get('path_inc', 'core/includes/path.inc');
   require_once DRUPAL_ROOT . '/core/includes/theme.inc';
   require_once DRUPAL_ROOT . '/core/includes/common.inc';
@@ -30,13 +31,6 @@ function _drupal_maintenance_theme() {
     $custom_theme = (isset($conf['maintenance_theme']) ? $conf['maintenance_theme'] : 'seven');
   }
   else {
-    // The bootstrap was not complete. So we are operating in a crippled
-    // environment, we need to bootstrap just enough to allow hook invocations
-    // to work. See _drupal_log_error().
-    if (!class_exists('Drupal\Core\Database\Database', FALSE)) {
-      require_once DRUPAL_ROOT . '/core/includes/database.inc';
-    }
-
     // We use the default theme as the maintenance theme. If a default theme
     // isn't specified in the database or in settings.php, we use Bartik.
     // @todo Should use the actual default theme configured, but that depends on
@@ -56,6 +50,9 @@ function _drupal_maintenance_theme() {
   }
 
   $themes = list_themes();
+  if (empty($themes) || !isset($themes[$custom_theme])) {
+    $themes = _system_rebuild_theme_data();
+  }
 
   // list_themes() triggers a drupal_alter() in maintenance mode, but we can't
   // let themes alter the .info data until we know a theme's base themes. So
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index ced66f4..5118087 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -194,48 +194,50 @@ function block_menu() {
  * Implements hook_menu_local_tasks_alter().
  */
 function block_menu_local_tasks_alter(&$data, $router_item, $root_path) {
-  if ($root_path == 'admin/structure/block' || strpos($root_path, 'admin/structure/block/list') === 0) {
-    // Replace the tab title of the default local task with the name of the
-    // default theme.
-    $themes = list_themes();
-    $default_theme = variable_get('theme_default', 'stark');
-    foreach ($data['tabs'][0] as $i => &$tab) {
-      if (isset($tab['#link']['path'])) {
-        if ($tab['#link']['path'] == 'admin/structure/block/list/default') {
-          $tab['#link']['title'] = $themes[$default_theme]->info['name'];
-        }
-        elseif ($tab['#link']['path'] == 'admin/structure/block/list/%') {
-          $selected_theme_index = $i;
-        }
+  if ($root_path === 'admin/structure/block' || $root_path === 'admin/structure/block/list/%') {
+    $tabs = &$data['tabs'][0]['output'];
+    // Determine the currently selected tab, if any.
+    $selected_index = -1;
+    $selected_id = '';
+    foreach ($tabs as $index => &$tab) {
+      if (isset($tab['#link']['path']) && $tab['#link']['path'] == 'admin/structure/block/list/%') {
+        $selected_index = $index;
+        $selected_id = $router_item['original_map'][4];
+        break;
       }
     }
-
     // Expand the dynamic %theme argument into a tab for each theme.
-    $selected_theme = isset($router_item['original_map'][4]) ? $router_item['original_map'][4] : NULL;
+    $themes = list_themes();
+    $default_theme = variable_get('theme_default', 'stark');
     foreach ($themes as $theme) {
       // The default theme is always exposed as default local task already.
       if ($theme->name === $default_theme) {
+        $tabs[0]['#link']['title'] = $theme->info['name'];
         continue;
       }
-      // If the current page shows the interface for a selected theme, then the
-      // menu router item with the %theme argument will expose the selected
-      // theme already; do not duplicate that tab, but ensure it appears in a
-      // consistent order when switching between tabs.
-      if ($theme->name === $selected_theme) {
-        $data['tabs'][0][] = $data['tabs'][0][$selected_theme_index];
-        unset($data['tabs'][0][$selected_theme_index]);
+      // If the current page is the active tab registered in hook_menu(), then
+      // the menu router item with the dynamic argument will be exposed already.
+      // We must not duplicate that tab, but in order to ensure that all of our
+      // tabs appear in a consistent order when switching between tabs, we need
+      // to re-inject it.
+      if ($theme->name === $selected_id) {
+        $tabs[$selected_index]['#link']['title'] = $theme->info['name'];
+        $tabs[] = $tabs[$selected_index];
+        unset($tabs[$selected_index]);
         continue;
       }
-      $data['tabs'][0][] = array(
+      $tabs[] = array(
         '#theme' => 'menu_local_task',
         '#link' => array(
           'title' => $theme->info['name'],
           'href' => 'admin/structure/block/list/' . $theme->name,
+          'localized_options' => array('html' => FALSE),
         ),
-        '#active' => $theme->name === $selected_theme,
-        '#weight' => $theme->name === $default_theme ? -10 : 0,
       );
     }
+    if (count($themes) > 1) {
+      $data['tabs'][0]['count']++;
+    }
   }
 }
 
diff --git a/core/modules/forum/forum.module b/core/modules/forum/forum.module
index 1bcb29c..459cbeb 100644
--- a/core/modules/forum/forum.module
+++ b/core/modules/forum/forum.module
@@ -209,7 +209,7 @@ function forum_menu_local_tasks_alter(&$data, $router_item, $root_path) {
           );
         }
       }
-      $data['actions'] = array_merge($data['actions'], $links);
+      $data['actions']['output'] = array_merge($data['actions']['output'], $links);
     }
   }
 }
diff --git a/core/modules/node/node.module b/core/modules/node/node.module
index bbb23e6..5c11424 100644
--- a/core/modules/node/node.module
+++ b/core/modules/node/node.module
@@ -1827,7 +1827,7 @@ function node_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   if ($root_path == 'admin/content') {
     $item = menu_get_item('node/add');
     if ($item['access']) {
-      $data['actions'][] = array(
+      $data['actions']['output'][] = array(
         '#theme' => 'menu_local_action',
         '#link' => $item,
       );
diff --git a/core/modules/system/system.api.php b/core/modules/system/system.api.php
index 2f3cdb1..2d09534 100644
--- a/core/modules/system/system.api.php
+++ b/core/modules/system/system.api.php
@@ -1084,10 +1084,17 @@ function hook_menu_link_delete($link) {
  *
  * @param $data
  *   An associative array containing:
- *   - actions: A list of of actions, each one being an associative array
- *     as described above.
- *   - tabs: A list of (up to 2) tab levels that contain a list of of tabs, each
- *     one being an associative array as described above.
+ *   - actions: An associative array containing:
+ *     - count: The amount of actions determined by the menu system, which can
+ *       be ignored.
+ *     - output: A list of of actions, each one being an associative array
+ *       as described above.
+ *   - tabs: An indexed array (list) of tab levels (up to 2 levels), each
+ *     containing an associative array:
+ *     - count: The amount of tabs determined by the menu system. This value
+ *       does not need to be altered if there is more than one tab.
+ *     - output: A list of of tabs, each one being an associative array as
+ *       described above.
  * @param $router_item
  *   The menu system router item of the page.
  * @param $root_path
@@ -1095,7 +1102,7 @@ function hook_menu_link_delete($link) {
  */
 function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   // Add an action linking to node/add to all pages.
-  $data['actions'][] = array(
+  $data['actions']['output'][] = array(
     '#theme' => 'menu_local_task',
     '#link' => array(
       'title' => t('Add new content'),
@@ -1109,7 +1116,7 @@ function hook_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   );
 
   // Add a tab linking to node/add to all pages.
-  $data['tabs'][0][] = array(
+  $data['tabs'][0]['output'][] = array(
     '#theme' => 'menu_local_task',
     '#link' => array(
       'title' => t('Example tab'),
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 358b9cf..68ccf7e 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -690,6 +690,7 @@ function system_menu() {
     'file' => 'system.admin.inc',
     'weight' => 20,
   );
+  // Theme configuration subtabs.
   $items['admin/appearance/settings/global'] = array(
     'title' => 'Global settings',
     'type' => MENU_DEFAULT_LOCAL_TASK,
@@ -1081,33 +1082,43 @@ function system_menu() {
  */
 function system_menu_local_tasks_alter(&$data, $router_item, $root_path) {
   if ($root_path === 'admin/appearance/settings' || $root_path === 'admin/appearance/settings/%') {
-    // Expand the dynamic %theme argument into a tab for each theme.
-    foreach ($data['tabs'][1] as $i => $tab) {
+    $tabs = &$data['tabs'][1]['output'];
+    // Determine the currently selected tab, if any.
+    $selected_index = -1;
+    $selected_id = '';
+    foreach ($tabs as $index => &$tab) {
       if (isset($tab['#link']['path']) && $tab['#link']['path'] == 'admin/appearance/settings/%') {
-        $selected_theme_index = $i;
+        $selected_index = $index;
+        $selected_id = $router_item['original_map'][3];
         break;
       }
     }
+    // Expand the dynamic %theme argument into a tab for each theme.
     $themes = list_themes();
-    $selected_theme = isset($router_item['original_map'][3]) ? $router_item['original_map'][3] : NULL;
     foreach ($themes as $theme) {
-      // If the current page shows the interface for a selected theme, then the
-      // menu router item with the %theme argument will expose the selected
-      // theme already; do not duplicate that tab, but ensure it appears in a
-      // consistent order when switching between tabs.
-      if ($theme->name === $selected_theme) {
-        $data['tabs'][1][] = $data['tabs'][1][$selected_theme_index];
-        unset($data['tabs'][1][$selected_theme_index]);
+      // If the current page is the active tab registered in hook_menu(), then
+      // the menu router item with the dynamic argument will be exposed already.
+      // We must not duplicate that tab, but in order to ensure that all of our
+      // tabs appear in a consistent order when switching between tabs, we need
+      // to re-inject it.
+      if ($theme->name === $selected_id) {
+        $tabs[$selected_index]['#link']['title'] = $theme->info['name'];
+        $tabs[] = $tabs[$selected_index];
+        unset($tabs[$selected_index]);
         continue;
       }
-      $data['tabs'][1][] = array(
+      $tabs[] = array(
         '#theme' => 'menu_local_task',
         '#link' => array(
           'title' => $theme->info['name'],
           'href' => 'admin/appearance/settings/' . $theme->name,
+          'localized_options' => array('html' => FALSE),
         ),
       );
     }
+    if (count($themes) > 1) {
+      $data['tabs'][1]['count']++;
+    }
   }
 }