I'm getting inconsistent marking of threads as read.
It looks like the forum icons wont turn gray until I go back into the forum to see all the threads are gray then go back to the main page...
After some testing it does appear the main page icon for a forum wont turn gray until I am on that forums list of threads having views all threads.
So if I go straight from what was my only unread thread to the main page, that forum (ie the pitstop) stays blue even though all threads have been read.