I have several contacts that were in my blackberry that when we moved the info over, and then sync'ed up the facebook contacts, there are several that are duplicates...I was able to successfully "join" them afterwards which might be your soution, to make a new contact then join them after.
i'm going to remove the fb sync then reinstall it because I think it's possible I didn't choose to combine fb contacts with existing contacts when I did it the first time.