On my iMac running Mountain Lion, Messages is chronically showing that I have 2 unread messages in its Dock icon. However there are no unread messages at all. I've even gone through and clicked on every single conversation in my history, just to make sure there wasn't some long-forgotten message floating around that hadn't been read.
It's not causing any major problems, but it is annoying to constantly think I've got a new message when i don't. Anyone know why this happens?