Its the way the forum software's core system works, it doesn't log every time you view a post it only logs it the first time (with no date/timestamp). So there is no way of being able to tell if you viewed the topic before or after the latest post, or how many times you have viewed it etc.
I am going to rip-apart and rewrite the core methods responsible for this behavior but it's going to take some time (the original code is a bloody nightmare!) so I though I would add the 'new' system as a temp fix rather than delaying the update.
