As a few of you have reported, there is a bug in the mechanism for marking forums/topics as read for some browsers (most complaints are about Chrome). We've changed some settings to use a different mechanism to perform this task and hopefully it will work properly for everyone now. Please post to this thread if you notice any anomalies.
A side effect of this is that you may find items now marked as unread that you had read and showed as such. This is a necessary side-effect of this system change and we apologize for the inconvenience.