How does that happen?
Sometimes when FR is having problems, when you submit a post, the post will be accepted into the system, but then the page will crash trying to refresh itself. This creates the false impression that the post didn't work. If you then do it again, thinking the first time didn't work, there will be a double post. This happened to me a few days ago.
But I didn’t do that, it went to preview and I posted.
Oh well!