I've posted this question to the forum's software developers and was told to change to a different type of database marking, which I did.
After making that adjustment it still doesn't seem to be working right
The next suggestion that tech support made was to suggest that I tell our users mark all forums as read to clear their existing new posts out the database. I tried it on my computer and it seemed to work for a while, but then it started getting wompy again.
To be honest after that I got sidetracked and haven't tried any other fixes. Now that you've reminded me I'll check back with tech support to see if they have any other suggestions.
Maybe you should try clicking the "Mark All Posts As Read" Link towards the bottom of the main forum page to see if that helps.
This link will also do it:
http://www.browncafe.com/forum/forumdisplay.php?do=markread