I'm having the same issue, Using Joomla 2.5.4 , Jomsocial 2.6.2 , JFBConnect 4.2.2, and Rocketttheme Tachyon template which uses gantry.
I tried to get over the problem by following Robby's suggestion, using the registration redirect plugin, which works fine for now...But with a problem that it is displaying a system message saying: "Redirected to Community registration" !!
Anyway, hope this issue will be solved asap with the next update. Although I'm using now JFBConnect 4.2.2, and you were talking about this problem here, and JFBConnect was at 4.2.1 !!!