Yeah, I noticed a bug with these forums that can get quite annoying, for example a topic will say its 10 pages long yet when I click on page 9 or 10 nothing is there just empty space with 0 posts and page is fully loaded, this tends not to be a problem in shorter threads though.
Yes, this happens because for some reason if there are comments deleted, it still counts that space as taken even after it is gone. Because in the longer topics that have had quite a few comments deleted, you will find more. The administrators are aware of this issue, and it should be taken care of soon hopefully.