Hey I get this too but I thought it was just cause I'm not so good at the computer stuff. But as close as I can tell sometimes(outside of being on here for a while)it depends on if you exit a thread by hitting your browser back button or by using the headings at the top:
Steelers Fever Forums
> Feedback & Support
> Steelers logo
Not 100% sure though.
Hey remember that bread crumb idea? Could this help out any?