Very strange. It might be because of secure cookies, which I've now disabled because apparently it isn't working as intended. If it keeps happening, let me know and I'll delve deeper.
In case anyone is wondering, I'm thinking it might be because you aren't normally browsing the forums with SSL on, which causes the secure cookie to throw a fit and stop working. It shouldn't have been throwing a fit, though, so I will look into that and see if this is a symptom of a different problem.