It happens to me using firefox.
I tend to open each part of the forum (general chat, openzaurus, etc.) one by one in the main window, then open any interesting topics in a new tab to look at after I\'ve scanned through the entire forum (hope that makes sense).
Normally after I get about half way down the list all of the topics are marked as read.
No idea. Bring on the new forum software! ;-)
Si