I was adding a comment to a question in Russian.SE and included two
@ references to notify two different users. When I attempted to submit the comment, I got a pop-up indicating that only one additional user can be notified with
Without explicitly closing the popup, I changed the text of the comment removing one of the
@ signs and then hit "enter" key to submit the comment. The comment was added and the popup disappeared.
Then I needed to add another comment to the same post, so I pressed "add comment" link and got a blank field to add the comment - with the same red popup still visible. In fact, it kept showing up until I explicitly closed it or navigated to another page. While it's not really a big deal, it's just strange to see a warning popup about the content of a comment when I haven't even started entering the comment.
EDIT: I'm working on a Linux Ubuntu 12.04 machine and this happens on Firefox 20, Chrome 26 and Chromium 25.
EDIT 2: Thanks to Sha Wiz Dow Ard, here's a short video demonstrating the bug.