Issue was reported in MDLQA-20124

I was able to reproduce it and it doesn't seem to have an existing bug report yet.

NOTE: This issue seems to be persistent for all pages that use the TinyMCE editor.

1. Access a course and add a Text and media area resource. 
2. In the TinyMCE editor, click the Multimedia icon.
3. Click on "Browse repositories".
4. Select "Upload a file".
5. Select an OGV file to upload.
6. In the Media details window, the preview box doesn't show the selected OGV video.
7. Click "Save".
8. Check the TinyMCE editor, the uploaded OGV file doesn't show either.
9. Click "Save and return to course".
10. The resource with OGV file was created and can be played.