Maybe its me but I think something in the forums cookie settings is causing it. Whenever you see threads with new posts its in bold text, after you've read the post/thread the text format is normal and not bold.
It doesnt seem to remember, when I check back later its like I didnt read those threads and the text looks bold again.
I have the same with posting, if I'm logged in and replying to a thread or posting and I wait too long and press submit then I get the login page again and whatever I was typing is lost.
Do more people have the same? Nothing has changed in my own local settings here concerning cookies so thats why I think its in the forum settings.