I've had the same issue, but with a total of 3 forums (Food Preparation, Being Raw, and Other Stuff). I used the Feedback link to let them know, but maybe a list of members who are having this problem all on this thread would be more helpful.
I've tried opening each thread, then marking all read for the individual forum. That clears it up within the forum, but nothing I have done will clear them from the main Forum menu. It's not a major problem for me, just a little glitch.