core/modules/ckeditor/js/views/ControllerView.js | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/core/modules/ckeditor/js/views/ControllerView.js b/core/modules/ckeditor/js/views/ControllerView.js
index 6234be1..7cfaeee 100644
--- a/core/modules/ckeditor/js/views/ControllerView.js
+++ b/core/modules/ckeditor/js/views/ControllerView.js
@@ -221,6 +221,8 @@
       // the feature that was just added or removed. Not every feature has
       // such metadata.
       var featureName = this.model.get('buttonsToFeatures')[button.toLowerCase()];
+      // Features without an associated command do not have a 'feature name' by
+      // default, so we use the lowercased button name instead.
       if (!featureName) {
         featureName = button.toLowerCase();
       }