It happened to me the other day as well. When you edit a post it seems to remove it from the Active Discussions and as well as not showing it as one of the most recent posts under the relevant topic, but if one opened the topic section you'll see the post at the bottom but showing that nobody has posted to it. So when I see "no posts" in a topic I know there's a post from someone in the section. There's seems to be a problem when editing a post. But when someone remoderates it it will appear as normal.