Try the following Rick, I can repeat this from any location. I just tried a remote machine, it is always reproducible.
I'm on 10.5.8 with Safari 5, and the most recent Firefox, does it in both, the remote machine is 10.3.9 with Safari 1.3.1
Copy this link http://forums.applecentral.com/ubbthreads.php/forums/29/1/Removed_Offers
Only Mods and Admins can get there so it won't do anyone else any good to try it.
Log out of the forums. Paste the link and try to go there, it will bring up the log in window. Log in, it takes you to the Removed Offers forum. Click on the main Forums link, all posts show unread.
If you log out and back in it doesn't show all posts as unread anymore, and the posts you really didn't read still show as unread, so when it fixes itself it shows the total post count correctly. BTW, this is in the main forum list only, when you click into a forum it doesn't show all posts unread. Clicking back to the main forum list then shows all the posts in the previous forum as read, but all the rest of the forums still show as all posts unread.
Also, I started a reply to a post. I left the tab open, for an hour ? or so without finishing the reply. After I finished the reply, when I clicked back to the forum list, all posts showed unread. I quit Safari and relaunched it and it was fine, all the unread posts were not marked as such anymore, and forums that had posts I didn't read show the correct amount unread, this is fairly repeatable for me.