diff --git a/core/modules/block/block.admin.inc b/core/modules/block/block.admin.inc
index 4863a56..2259176 100644
--- a/core/modules/block/block.admin.inc
+++ b/core/modules/block/block.admin.inc
@@ -5,6 +5,8 @@
  * Admin page callbacks for the block module.
  */
 
+use Drupal\block\Plugin\Core\Entity\Block;
+
 /**
  * Page callback: Attaches CSS for the block region demo.
  *
@@ -190,7 +192,7 @@ function block_admin_display_form_submit($form, &$form_state) {
  *
  * Callback for usort() in block_admin_display_prepare_blocks().
  */
-function _block_compare($a, $b) {
+function _block_compare(Block $a, Block $b) {
   global $theme_key;
 
   // Theme should be set before calling this function, or the current theme
@@ -262,6 +264,24 @@ function block_admin_add($plugin_id, $theme = NULL) {
  */
 function block_admin_edit($entity_id) {
   $entity = entity_load('block', $entity_id);
+
+  // Get the theme for the page title.
+  $admin_theme = config('system.theme')->get('admin');
+  $themes = list_themes();
+  $theme_key = $entity->get('theme');
+  $theme = $themes[$theme_key];
+  // Use meaningful titles for the main site and administrative themes.
+  $theme_title = $theme->info['name'];
+  if ($theme_key == variable_get('theme_default', 'stark')) {
+    $theme_title = t('!theme (default theme)', array('!theme' => $theme_title));
+  }
+  elseif ($admin_theme && $theme_key == $admin_theme) {
+    $theme_title = t('!theme (administration theme)', array('!theme' => $theme_title));
+  }
+
+  // Get the block subject for the page title.
+  drupal_set_title(t("%label block in %theme", array('%label' => $entity->label(), '%theme' => $theme_title)), PASS_THROUGH);
+
   return entity_get_form($entity);
 }
 
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index be07557..3763584 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -131,7 +131,7 @@ function block_menu() {
   $items['admin/structure/block/manage/%'] = array(
     'title' => 'Configure block',
     'page callback' => 'block_admin_edit',
-    'page arguments' => array(4, 5),
+    'page arguments' => array(4),
     'access arguments' => array('administer blocks'),
     'file' => 'block.admin.inc',
   );
@@ -143,7 +143,7 @@ function block_menu() {
   $items['admin/structure/block/manage/%/delete'] = array(
     'title' => 'Delete block',
     'page callback' => 'drupal_get_form',
-    'page arguments' => array('block_admin_block_delete', 4, 5),
+    'page arguments' => array('block_admin_block_delete', 4),
     'access arguments' => array('administer blocks'),
     'type' => MENU_LOCAL_TASK,
     'context' => MENU_CONTEXT_NONE,
@@ -317,7 +317,7 @@ function _block_get_renderable_region($list = array()) {
     if ($not_cacheable || in_array($block->get('cache'), array(DRUPAL_NO_CACHE, DRUPAL_CACHE_CUSTOM))) {
       // Non-cached blocks get built immediately.
       if ($block->access()) {
-        $build[$key] = entity_view($block, 'full');
+        $build[$key] = entity_view($block, 'block');
       }
     }
     else {
@@ -476,7 +476,7 @@ function _block_get_renderable_block($element) {
   $block = $element['#block'];
   // Don't bother to build blocks that aren't accessible.
   if ($element['#access'] = $block->access()) {
-    $element += entity_view($block, 'full');
+    $element += entity_view($block, 'block');
   }
   return $element;
 }
diff --git a/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/block/block/CustomBlock.php b/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/block/block/CustomBlock.php
index 3113bfe..37b11d4 100644
--- a/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/block/block/CustomBlock.php
+++ b/core/modules/block/custom_block/lib/Drupal/custom_block/Plugin/block/block/CustomBlock.php
@@ -72,6 +72,19 @@ public function blockForm($form, &$form_state) {
   }
 
   /**
+   * Overrides \Drupal\block\BlockBase::blockValidate().
+   */
+  public function blockValidate($form, &$form_state) {
+    $custom_block_exists = (bool) db_query_range('SELECT 1 FROM {block_custom} WHERE bid <> :bid AND info = :info', 0, 1, array(
+      ':bid' => $form_state['values']['delta'],
+      ':info' => $form_state['values']['info'],
+    ))->fetchField();
+    if (empty($form_state['values']['info']) || $custom_block_exists) {
+      form_set_error('info', t('Ensure that each block description is unique.'));
+    }
+  }
+
+  /**
    * Overrides \Drupal\block\BlockBase::blockSubmit().
    */
   public function blockSubmit($form, &$form_state) {
diff --git a/core/modules/block/lib/Drupal/block/BlockFormController.php b/core/modules/block/lib/Drupal/block/BlockFormController.php
index bf28b0f..8053279 100644
--- a/core/modules/block/lib/Drupal/block/BlockFormController.php
+++ b/core/modules/block/lib/Drupal/block/BlockFormController.php
@@ -29,25 +29,6 @@ public function form(array $form, array &$form_state, EntityInterface $entity) {
       '#value' => $entity->id(),
     );
 
-    // Get the theme for the page title.
-    $admin_theme = config('system.theme')->get('admin');
-    $themes = list_themes();
-    $theme_key = $entity->get('theme');
-    $theme = $themes[$theme_key];
-    // Use meaningful titles for the main site and administrative themes.
-    $theme_title = $theme->info['name'];
-    if ($theme_key == variable_get('theme_default', 'stark')) {
-      $theme_title = t('!theme (default theme)', array('!theme' => $theme_title));
-    }
-    elseif ($admin_theme && $theme_key == $admin_theme) {
-      $theme_title = t('!theme (administration theme)', array('!theme' => $theme_title));
-    }
-
-    // Get the block subject for the page title.
-    if ($label = $entity->label()) {
-      drupal_set_title(t("%label block in %theme", array('%label' => $label, '%theme' => $theme_title)), PASS_THROUGH);
-    }
-
     $form['settings'] = array(
       '#weight' => -5,
     );
@@ -74,7 +55,7 @@ public function form(array $form, array &$form_state, EntityInterface $entity) {
       '#description' => t('Select the region where this block should be displayed.'),
       '#default_value' => $entity->get('region'),
       '#empty_value' => BLOCK_REGION_NONE,
-      '#options' => system_region_list($theme_key, REGIONS_VISIBLE),
+      '#options' => system_region_list($entity->get('theme'), REGIONS_VISIBLE),
     );
 
     // Visibility settings.
@@ -234,15 +215,6 @@ public function validate(array $form, array &$form_state) {
       $config_id = explode('.', $form_state['values']['machine_name']);
       $form_state['values']['machine_name'] = array_pop($config_id);
     }
-    if ($form_state['values']['module'] == 'block') {
-      $custom_block_exists = (bool) db_query_range('SELECT 1 FROM {block_custom} WHERE bid <> :bid AND info = :info', 0, 1, array(
-        ':bid' => $form_state['values']['delta'],
-        ':info' => $form_state['values']['info'],
-      ))->fetchField();
-      if (empty($form_state['values']['info']) || $custom_block_exists) {
-        form_set_error('info', t('Ensure that each block description is unique.'));
-      }
-    }
     $form_state['values']['visibility']['role']['roles'] = array_filter($form_state['values']['visibility']['role']['roles']);
     $entity = $this->getEntity($form_state);
     if ($entity->isNew()) {
diff --git a/core/modules/block/lib/Drupal/block/BlockRenderController.php b/core/modules/block/lib/Drupal/block/BlockRenderController.php
index f5ae699..82134c6 100644
--- a/core/modules/block/lib/Drupal/block/BlockRenderController.php
+++ b/core/modules/block/lib/Drupal/block/BlockRenderController.php
@@ -37,9 +37,11 @@ public function buildContent(array $entities, array $displays, $view_mode, $lang
    *   An array of defaults to add into the entity render array.
    */
   protected function getBuildDefaults(EntityInterface $entity, $view_mode, $langcode) {
-    // @todo Added to facilitate the possibly bogus assertion in
-    //   \Drupal\block\Tests\BlockTest::testCustomBlock().
-    if ($view_mode != 'full') {
+    // @todo \Drupal\block\Tests\BlockTest::testCustomBlock() assuemes that a
+    //   block can be rendered without any of its wrappers. To do so, it uses a
+    //   custom view mode, and we choose to only add the wrappers on the default
+    //   view mode, 'block'.
+    if ($view_mode != 'block') {
       return array();
     }
 
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
index 274ddb2..ffc8d0f 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
@@ -117,8 +117,11 @@ public function testCustomBlock() {
     // Confirm that the custom block has been created, and then query the created bid.
     $this->assertText(t('The block configuration has been saved.'), 'Custom block successfully created.');
 
-    // Check that block_block_view() returns the correct title and content.
-    $data = entity_view($block, 'teaser');
+    // Check that entity_view() returns the correct title and content.
+    // @todo This assumes that a block's content can be rendered without its
+    //   wrappers. If this is a reasonable expectation, it should be documented
+    //   elsewhere.
+    $data = entity_view($block, 'content');
     $definition = $block->getPlugin()->getDefinition();
     $config = $definition['settings'];
     $this->assertEqual(check_markup($custom_block['body[value]'], $config['format']), render($data), 'BlockInterface::build() provides correct block content.');
diff --git a/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php b/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
index cc96397..d4c3379 100644
--- a/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
+++ b/core/modules/user/lib/Drupal/user/Tests/UserBlocksTests.php
@@ -99,7 +99,7 @@ function testWhosOnlineBlock() {
     $this->updateAccess($this->adminUser->uid, $inactive_time);
 
     // Test block output.
-    $content = entity_view($block, 'full');
+    $content = entity_view($block, 'block');
     $this->drupalSetContent(render($content));
     $this->assertRaw(t('2 users'), 'Correct number of online users (2 users).');
     $this->assertText($user1->name, 'Active user 1 found in online list.');