I've noticed this lately. You post a reply on a thread, but NOT on the last page of the thread (if it's multi-page). You never see your reply posted (e.g., the latest page loads showing your post as the very last one in the thread). Instead, the current page reloads WITH the reply box still displayed as if you just finished entering your post but never hit "submit." If you keep hitting "submit," there will be multiple posts on the last page, but it keeps reloading the current page as I just described. I actually have to CTRL-A, CTRL-C (to save what I wrote) and then go to the last page to make sure my post was saved.
I'm using Firefox, but I do use plug ins like NoScript. Priuschat is allowed, but perhaps there's another plugin I shouldn't be blocking?