Nothing broken, I suspect. If you have your view set to "threaded" then your favorites will also be logged that way. The "new" posts shown will be the sum of the posts in new threads that you haven't read. Any new posts in older threads won't show up.

If you set your view to "unthreaded", it's just chronological and all new unread posts will be indicated in the count.

Go to the board and hit the unthreaded link. Then check the favorites list and you'll see that the count has changed.