When the forum software appears to be acting strangely, we advise people to log out of the forums, delete all cookies for macrumors.com and forums.macrumors.com, and then log back in. Sometimes that solves the problem.
For diagnostic reasons, you can change web browsers and see if the problem continues, as a way to determine if the problem is specific to one browser (and its cookies) or is system-wide. In the same way, using another computer, if one is available, would tell you if the problem is about something on that one computer or if it's something about your MacRumors account and the way the forum software works.