I have to play with that...usually, it should only take you to the last page if you have all the other posts/pages marked as read. So if you, for instance, marked all forums as read, then someone posts in a thread that you haven't read before, it might take you to that post.
That could be a result of the conversion, sometimes when a conversion takes place it doesn't "remember" what you have and have not read, and sometimes it might end up automatically marking everything as read so you start from a "clean slate" Not sure if this is what happened or not. But if so, then if there was a thread that was 200 pages long and you had never read it, then someone posted to it after the conversion, it would take you to that post. Not saying that is what is happening but that could explain it.