This has happened to me twice in the last day or two. I had a tab open to a Pagure issue. I tried to add a comment, but apparently my session was stale, so Pagure decided to run through the login process automatically. Great - except it then went back to the issue page with an Invalid method: GET error showing, and my comment had disappeared. It was not added to the issue, and it's no longer shown in the edit box. Going 'back' doesn't recover it into the edit box either.

This is on the pagure.io instance.