[yubiox]

The calendar has been broken for a while now. It is impossible to close reminder popups, neither button does anything. It doesn't sync properly anymore either. I wish there was undo when you accidentally click the subject header and it sorts by subject. It is really hard to get back to sort by date then unread.

[mdaniel]

I don't use the calendar integration, but the behavior you're describing is almost certainly some JS explosion that wasn't handled. "Tools > Developer Tools > Error Console" (Ctrl-Shift-J in my copy) may cough up something that would enable you to file a bug report, if you were inclined, or may even help understand what expectation it had that your setup deviates from