Steps to reproduce the error:

1. Create a matching question in question bank
2. Click on expand all link
3. Within combined feedback element, tinymce is not writeable and default value for feedback is not display.
4. Select the toolbar toggle, tinymce is now writeable and default value for feedback is display.

Note that this is only a way to reproduce the bug, but that the problem is everywhere in Moodle when there is an editor in a collapsed section.
Also the fact that the current content of the editor is not displayed in the editor when the section is expanded is a very severe bug as the user can think it is empty !!