IF you go and read either of these two threads.
viewtopic.php?f=21&t=4085&start=15
viewtopic.php?f=4&t=4080&start=15
You will find quotes of posts not showing in the thread. That is because on each of them the 15th reply ended up not posting into the actual thread. In both cases the post was also written by the thread originator. You can however still read the vanished posts in the thread review pane when writing a response to the thread.
I really hope these are the only two places that this has happened in.