diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index 6466b60..5fc7c6a 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -363,6 +363,7 @@ function _block_rehash($theme = NULL) {
   $block_configs = config_get_storage_names_with_prefix('plugin.core.block.' . $theme);
   $regions = system_region_list($theme);
   foreach ($block_configs as $config) {
+    // Only list valid block instances.
     if (!$block = block_load($config)) {
       continue;
     }
@@ -477,15 +478,20 @@ function block_list($region) {
  *
  * @return
  *   A block object.
+ *
+ * @todo Add block_load_multiple() and make this function a single-value wrapper.
  */
 function block_load($plugin_id, array $conf = array()) {
   $manager = drupal_container()->get('plugin.manager.block');
   if (!$block = $manager->getInstance(array('config' => $plugin_id))) {
+    // If the block instance does not exist, try to create it.
     try {
       $block = $manager->createInstance($plugin_id, $conf);
     }
     catch (PluginException $e) {
       $config = config($plugin_id)->get();
+      // Ignore blocks belonging to disabled modules, but re-throw valid
+      // exceptions when the module is enabled and the plugin is misconfigured.
       if (module_exists($config['module'])) {
         throw $e;
       }
@@ -500,6 +506,8 @@ function block_load($plugin_id, array $conf = array()) {
  *
  * @return
  *   An array of blocks grouped by region.
+ *
+ * @todo Remove this function, and replace it with a block_load_multiple().
  */
 function _block_load_blocks() {
   global $theme;
@@ -513,6 +521,8 @@ function _block_load_blocks() {
     }
     else {
       $config = config($plugin_id)->get();
+      // Ignore blocks belonging to disabled modules, but re-throw valid
+      // exceptions when the module is enabled and the plugin is misconfigured.
       if (module_exists($config['module'])) {
         throw new PluginException(sprintf('The plugin %s was not found.', $plugin_id));
       }
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
index 8c8ddde..7928fa9 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockTest.php
@@ -381,7 +381,7 @@ function testBlockRehash() {
   }
 
   /**
-   * Test disabled blocks.
+   * Tests blocks belonging to disabled modules.
    */
   function testBlockModuleDisable() {
     module_enable(array('block_test'));
@@ -400,10 +400,22 @@ function testBlockModuleDisable() {
     $block['region'] = 'header';
     $this->drupalPost('admin/structure/block/manage/' . $block['id'] . '/' . $block['theme'], array('machine_name' => $block['machine_name'], 'region' => $block['region']), t('Save block'));
 
+    // Disable the block test module and refresh the definitions cache.
     module_disable(array('block_test'), FALSE);
+    $manager->clearCachedDefinitions();
+
+    // Ensure that the block administration page still functions as expected.
     $this->drupalGet('admin/structure/block');
     $this->assertResponse(200);
-    $this->assertTitle('Blocks');
+    // A 200 response is possible with a fatal error, so check the title too.
+    $this->assertTitle(t('Blocks | Drupal'));
+
+    // Ensure that the disabled module's block instance is not listed.
+    $this->assertNoText(t('Test block caching'));
+
+    // Ensure that the disabled module's block plugin is no longer available.
+    $this->drupalGet('admin/structure/block/list/block_plugin_ui:' . variable_get('theme_default', 'stark') . '/add');
+    $this->assertNoText(t('Test block caching'));
   }
 
 }