I am going to be reading the answers you get, because this happens to me, too, and I don't know why. I do note that logging out of another account will kick me out of accounts on different tabs, but sometimes-not-always. And the gmail notifier seems involved. Again, it's easier for me to log back in than to make the effort to figure things out, but I'll happily accept an explanation from someone else who know more/better. C'mon, people, we're waiting!
