Anchor disappears when dropped into widget editable region

[kkrzton]

Steps to reproduce

1. Go to ​http://ckeditor.com/demo#widgets.
2. Use 3rd editor (Enhanced Image), switch to source mode and paste HTML

   <p>Example text <a id="anchor" name="anchor"></a></p>
   
   <figure class="image" style="float:right"><img alt="Apollo-CSM-LM" src="http://c.cksource.com/a/1/img/demo/apollo-csm-lm.png" width="200" />
   <figcaption>Apollo CMS-LM spacecraft</figcaption>
   </figure>
   

3. Switch back to WYSIWYG mode.
4. Drag and drop anchor into image description.

Actual result

The anchor can be drag and dropped into editable. When dropped it disappears (probably because of ACF applied to editable region).

Expected result

Not sure exactly what should happen, I assume the anchor should be not droppable if it's going to be removed anyway.

Other details (browser, OS, CKEditor version, installed plugins)

Tested on Chrome.