to repropduce:

1. open the bugtracker, click tos ome other bages, and then go back to be able to press the forward button.
2. start typing a comment (don't leave it, and ensure it contains any text).
3. press forward button
4. press cancel in the notification that changes will be lost
5. see the result.

EDIT: I can't reproduce anymore, and I didn't take any screenshots.