I just registered, and saw what you meant. The problem, I think, is how you have your new-user redirect setup. It's going to the "Registration Page", but since JFBConnect has created the user and logged them in, when you go to that page, JomSocial is not letting them register because they already have an account.
Instead of redirecting the user to the registration page, you should create a menu item (External Link type) to the following URL:
index.php?option=com_community&view=profile&task=edit
Then, you can set the JFBConnect new user redirection to go to that page, and I think your problem should be fixed. Hope that makes sense, but if not, just let us know and we'll help you out.
Thanks, and good luck!