This was discovered while testing https://tracker.moodle.org/browse/MDLQA-15183.

 Steps to reproduce:

1. Login as Admin.
2. Create a Course.
3. Create a Forum in the Course.
4. Add a discussion topic in the Forum.
   1. Add a subject.
   2. In the "Message" text area, click the Insert Media icon.
   3. Click the "Audio" tab
   4. Browse and upload an mp3 file from your computer.
   5. Click Insert media.
   6. Click Post to forum.
5. Go back to the created discussion.
6. Edit the discussion.
7. In the "Message" are, click the mp3 file, then the media button.

Expected: After you click on the media button, you should the see "Insert media" popup with the "Audio" tab activated and populated with the mp3 file info.

Actual: After you click on the media button, the "Insert media" is displayed in the same manner as when adding a new resource. The audio tab is not populated with the mp3 file info.