Threads keep coming back as new, even though

I read the thread, cycled through to the main menu through the links (not the back button), look again, and low and behold the thread is still showing unread? In fact, I get email from subscribing to the thread over and over about the same post (Not always). Now I understand that if somebody goes back and edits a post in that thread it will send email for susbscription it will show it as unread, but most the time nothing has changed? This has only recently started happening.
Help?
-Bruce