diff --git a/core/modules/block/block.api.php b/core/modules/block/block.api.php
index 93e90df..aa915a3 100644
--- a/core/modules/block/block.api.php
+++ b/core/modules/block/block.api.php
@@ -48,11 +48,11 @@ function hook_block_view_alter(array &$build, \Drupal\block\BlockPluginInterface
  *
  * In this hook name, BASE_BLOCK_ID refers to the block implementation's plugin
  * id, regardless of whether the plugin supports derivatives. For example, for
- * the \Drupal\system\Plugin\block\block\SystemPoweredByBlock block, this would
- * be 'system_powered_by_block' as per that class's annotation. And for the
- * \Drupal\menu\Plugin\Block\MenuBlock block, it would be 'system_menu_block' as
- * per that class's annotation, regardless of which menu the derived block is
- * for.
+ * the \Drupal\system\Plugin\Block\SystemPoweredByBlock block, this would be
+ * 'system_powered_by_block' as per that class's annotation. And for the
+ * \Drupal\system\Plugin\Block\SystemMenuBlock block, it would be
+ * 'system_menu_block' as per that class's annotation, regardless of which menu
+ * the derived block is for.
  *
  * @param array $build
  *   A renderable array of data, as returned from the build() implementation of
diff --git a/core/modules/menu/menu.module b/core/modules/menu/menu.module
index bca49fc..57f39b6 100644
--- a/core/modules/menu/menu.module
+++ b/core/modules/menu/menu.module
@@ -387,6 +387,7 @@ function _menu_parents_recurse($tree, $menu_name, $indent, &$options, $exclude,
 function menu_block_view_system_menu_block_alter(array &$build, BlockPluginInterface $block) {
   // Add contextual links for system menu blocks.
   $menus = menu_list_system_menus();
+  // @todo Clean up when http://drupal.org/node/1874498 lands.
   list(, $menu_name) = explode(':', $block->getPluginId());
   if (isset($menus[$menu_name]) && isset($build['content'])) {
     foreach (element_children($build['content']) as $key) {
diff --git a/core/modules/system/lib/Drupal/system/Entity/Menu.php b/core/modules/system/lib/Drupal/system/Entity/Menu.php
index 8e295b2..29a838f 100644
--- a/core/modules/system/lib/Drupal/system/Entity/Menu.php
+++ b/core/modules/system/lib/Drupal/system/Entity/Menu.php
@@ -73,7 +73,8 @@ class Menu extends ConfigEntityBase implements MenuInterface {
    */
   public function getExportProperties() {
     $properties = parent::getExportProperties();
-    // @todo Make $description protected and include it here.
+    // @todo Make $description protected and include it here, see
+    //   https://drupal.org/node/1301106.
     $names = array(
       'locked',
     );
diff --git a/core/modules/system/lib/Drupal/system/Plugin/Block/MenuBlock.php b/core/modules/system/lib/Drupal/system/Plugin/Block/SystemMenuBlock.php
similarity index 66%
rename from core/modules/system/lib/Drupal/system/Plugin/Block/MenuBlock.php
rename to core/modules/system/lib/Drupal/system/Plugin/Block/SystemMenuBlock.php
index bd940d9..c6bf324 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/Block/MenuBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/Block/SystemMenuBlock.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\system\Plugin\Block\MenuBlock.
+ * Contains \Drupal\system\Plugin\Block\SystemMenuBlock.
  */
 
 namespace Drupal\system\Plugin\Block;
@@ -18,16 +18,16 @@
  *   id = "system_menu_block",
  *   admin_label = @Translation("Menu"),
  *   category = "menu",
- *   derivative = "Drupal\system\Plugin\Derivative\MenuBlock"
+ *   derivative = "Drupal\system\Plugin\Derivative\SystemMenuBlock"
  * )
  */
-class MenuBlock extends BlockBase {
+class SystemMenuBlock extends BlockBase {
 
   /**
    * Overrides \Drupal\block\BlockBase::access().
    */
   public function access() {
-    // @todo The 'Tools' menu should be available to anonymous users.
+    // @todo Clean up when http://drupal.org/node/1874498 lands.
     list( , $derivative) = explode(':', $this->getPluginId());
     return ($GLOBALS['user']->isAuthenticated() || in_array($derivative, array('main', 'tools', 'footer')));
   }
@@ -36,7 +36,8 @@ public function access() {
    * {@inheritdoc}
    */
   public function build() {
-    list($plugin, $menu) = explode(':', $this->getPluginId());
+    // @todo Clean up when http://drupal.org/node/1874498 lands.
+    list(, $menu) = explode(':', $this->getPluginId());
     return menu_tree($menu);
   }
 
diff --git a/core/modules/system/lib/Drupal/system/Plugin/Derivative/MenuBlock.php b/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
similarity index 85%
rename from core/modules/system/lib/Drupal/system/Plugin/Derivative/MenuBlock.php
rename to core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
index c005019..5542808 100644
--- a/core/modules/system/lib/Drupal/system/Plugin/Derivative/MenuBlock.php
+++ b/core/modules/system/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php
@@ -2,7 +2,7 @@
 
 /**
  * @file
- * Contains \Drupal\system\Plugin\Derivative\MenuBlock.
+ * Contains \Drupal\system\Plugin\Derivative\SystemMenuBlock.
  */
 
 namespace Drupal\system\Plugin\Derivative;
@@ -15,9 +15,9 @@
 /**
  * Provides block plugin definitions for custom menus.
  *
- * @see \Drupal\system\Plugin\block\block\MenuBlock
+ * @see \Drupal\system\Plugin\Block\SystemMenuBlock
  */
-class MenuBlock extends DerivativeBase implements ContainerDerivativeInterface {
+class SystemMenuBlock extends DerivativeBase implements ContainerDerivativeInterface {
 
   /**
    * The menu storage.
@@ -27,7 +27,7 @@ class MenuBlock extends DerivativeBase implements ContainerDerivativeInterface {
   protected $menuStorage;
 
   /**
-   * Constructs new MenuBlock.
+   * Constructs new SystemMenuBlock.
    *
    * @param \Drupal\Core\Entity\EntityStorageControllerInterface $menu_storage
    *   The menu storage.
diff --git a/core/modules/system/system.module b/core/modules/system/system.module
index 4b5afba..39886f4 100644
--- a/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -9,7 +9,6 @@
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Utility\ModuleInfo;
-use Drupal\system\Plugin\Block\SystemMenuBlock;
 use Drupal\user\UserInterface;
 use Symfony\Component\HttpFoundation\JsonResponse;
 use Symfony\Component\HttpFoundation\RedirectResponse;
@@ -2283,6 +2282,7 @@ function system_user_timezone(&$form, &$form_state) {
  */
 function system_preprocess_block(&$variables) {
   // Derive the base plugin ID.
+  // @todo Clean up when http://drupal.org/node/1874498 lands.
   list($plugin_id, $derivative) = explode(':', $variables['plugin_id'] . ':');
   switch ($plugin_id) {
     case 'system_powered_by_block':