Hmm, that's a new one on me. So the thread, as listed in the forum index, will show a recent post, but when you click on it, it's not there? Or do you notice an own post simply not appearing?
Could people please notify me immediately if you see a post disappear? If it is something happening regularly, I want to see if there is a pattern. Either someone is doing something they shouldn't be able to for kicks, or there's a database problem.