commit da182635e5c57676ad7d6621b40a0adc10c6d422
Author: Wim Leers <wim.leers@acquia.com>
Date:   Wed Jun 8 15:13:55 2016 +0200

    Ensure that the example is actually rendered.

diff --git a/core/modules/system/src/Controller/ComponentController.php b/core/modules/system/src/Controller/ComponentController.php
index 5cd9c7c..230921f 100644
--- a/core/modules/system/src/Controller/ComponentController.php
+++ b/core/modules/system/src/Controller/ComponentController.php
@@ -122,6 +122,7 @@ protected function doListComponents(array $components) {
         $component_build_preview_to_be_rendered = $component_build_preview;
         $rendered_preview = \Drupal::service('renderer')->renderPlain($component_build_preview_to_be_rendered);
       }
+      \Drupal::service('renderer')->renderRoot($component_build);
 
       $build[$component_name] = [
         'header' => [
@@ -137,7 +138,10 @@ protected function doListComponents(array $components) {
             '#prefix' => Markup::create('<div style="padding:1em;margin-left:3em;">'),
             '#type' => 'fieldset',
             '#attributes' => ['style' => 'padding:1em;'],
-            'example' => $component_build,
+            'example' => [
+              '#markup' => $component_build['#markup'],
+              '#attached' => $component_build['#attached'],
+            ],
           ],
           'markup' => [
             '#prefix' => '<pre><code>',