Why does Messages on OSX always show unread messages? 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?
I have been getting this on OS X 10.10 (Yosemite). I found a solution in the Apple discussion forums.

User LHindiii there recommended quitting Messages.app then using Activity Monitor to quit the Dock (which will automatically relaunch) and this worked for me.