It shouldn't - I'm pretty sure that "Mark forum read" will update your read stats with the current time WHEN you click on the link. Perhaps you need to refresh your cache next time you visit the forum?
Next time you're in a forum, check the clock on the upper right - if it's not your current time (assuming you've properly set your time zone), refresh the page and see if things look a bit different.
If you keep having problems, send me a private message or email.
So, I can't read this message from Captain Cuba, because it says that his instant rating is negative 1.74, which is below my threshold of zero. When I check his profile to see what's up, his threshold is now 109.5 (well above my threshold ).