I have have a similar problem. I sign in with Facebook, then type in my comment and click on “post it”. Next, the page reloads, my comment isn’t anywhere to be seen (not even in admin panel) and a label saying “Comment” is shown next to the comment text area.
I gave it one more try and typed in my comment again. After a click on “post it”, this time the comment surprisingly was shown.
The problem is… I can’t tell all blog commentors to type in their comment twice…