Yea, it has always been that way for me. It doesn't seem to have anytyhing to do with wether or not you have actually read them or not.. it is more like "new psots since last visit" and even wrose it has nothign to do with your account, but the computer itself i find.
so, if I visit logged out or logged in, the effect is the same. If i log in from a different computer, tons of stuff is unread.
Basically, it is downright broken which is unfortunate since it'd be a great feature to have. In all honesty, I dislike whatever is driving this forum. My built-in firefox spell checker doesn't work in this edit box and I've never seen that before.