Haven't noticed this on any other account, but I have three PMs in specific (my most recent PMs), that, even though I've read them, they keep popping up when I hover over my inbox. And they continue to do so. I'll click on it to open the PM and within seconds, it'll show up again unread. It'll stop for a couple of minutes and then continue. It's really frustrating.
Using Google Chrome and Windows 7.