Gigi, it seems to be because going to the front page of the site basically "marks you present" and so when you go to the forum page the web server thinks you've already been there and so doesn't mark anything as new. You could try going straight to clown-forum.com/forum for now, that should make the new post icons reappear. (If not, let me know and I'll teach you The Cookie Dance.)
I'm also going to try a few things to see if I can get it to behave properly tonight; if not, I might get rid of the "Latest Posts" box on the front page to see if that does the trick.