Unable to set Link URL in Media Editor

[volleyballmaniac]

1. Open a post

2. Upload image into it & save post

3. Re-open Media Editor & click on "Gallery"

4. Attempt to edit/change the image's "Link URL" to anything (even none).

5. Click "Save all changes"

-> Link URL reverts back to "File URL"

So the symptom is that Link URL is not settable.

I noticed that if I go into HTML view and delete the rel="attachment wp-att-507" tag I WAS able to update the link URL.

See #13429