See here:

https://pagure.io/fedora-workstation/issue/131#comment-628169

Notice that Neal accidentally removes the meeting-request tag from the issue, then tags it again. Then I do the same. The problem is that when I started typing my comment, the tag was not present in the issue. By the time I finished typing my comment, Neal had added the tag back. I had not intended to modify the tags at all with my comment. Pagure removed the tag without my permission. I think that, when I leave a comment, it's resetting all tags to the state they were in at the time I first loaded the issue page.