I have to say I've never seen the issue/bug being discussed. I posted about it somewhere else, but if you mark a/all forums read or if an old thread is bumped up, you're going to get jumped into it even though you've never actually "read" it. The former is a situation where you're telling the system you've read it; the latter is mostly a technical limit (the data isn't kept around permanently as there's quite a lot of it).
The problem with trying to debug this situation (if it happens for reasons other than those) is that the act of seeing the issue manipulates the data (since the thread is now read). I'd literally have to be looking all all the data before someone hit the issue before I could say whether it is a bug, or if it's one of those things from above. If it happens and you tell me the thread it's happening with, then I might be able to make some guesses.
Of course, the key here is if we had a "go to first unread" button and the thread title itself, how often would you use the thread title (to go to the first post)? If you're using the title (and you've made a conscious decision), then it's a matter of clicking a different area than what you might've done on another software. If 99% of the time, you want to go to the first unread post (which is what I always do and I know other people do as well), then this focuses on the "normal" behavior that people have and exposes it more clearly, probably showing the behavior to more casual users that wouldn't have known about it in the first place.
The problem with trying to debug this situation (if it happens for reasons other than those) is that the act of seeing the issue manipulates the data (since the thread is now read). I'd literally have to be looking all all the data before someone hit the issue before I could say whether it is a bug, or if it's one of those things from above. If it happens and you tell me the thread it's happening with, then I might be able to make some guesses.
Of course, the key here is if we had a "go to first unread" button and the thread title itself, how often would you use the thread title (to go to the first post)? If you're using the title (and you've made a conscious decision), then it's a matter of clicking a different area than what you might've done on another software. If 99% of the time, you want to go to the first unread post (which is what I always do and I know other people do as well), then this focuses on the "normal" behavior that people have and exposes it more clearly, probably showing the behavior to more casual users that wouldn't have known about it in the first place.