Even though I just logged in. any help with this?
I believe the board software doesn't actually track "read" threads. It keeps a timestamp of the last time you were "caught up" and marks everthing after that time as "read." When you log in, the timestamp is reset, so everything appears as read. Something else happens every so often and resets the timestamp, even if you don't log off and back on.
(At least that's my best explanation of the behaviour I've seen.)
More informed info welcome.