We're working on JFBConnect today. We'll test further with the scenario you mention below (it's actually not a commonly used one, from the reports we've gotten). If we find a cause and/or are able to reproduce, we'll let you know.
Yes, the usermapping should handle keeping users in-sync with their CB profiles. CB does some strange things though depending on how it's configured, and we might have missed something.
Facebook login fails after user edits profile
