Just wanted to update you. We've found the cause of this problem and it will be in the next release (hopefully by the end of this week).
If you're looking to try this on your own to test first (always appreciated to get feedback before we push out a release), do the following:
In the file /components/com_jfbconnect/helpers/facebookhelper.php, around line 146 look for the following line:
$mainframe->enqueueMessage("You were successfully logged back in using your Facebook credentials");
Change the lines underneath it to:
$return = base64_decode(JRequest::getVar('return'));
$mainframe->redirect(JRoute::_($return));
It would work for some people, in certain scenerios before, but this should fix it so it works for everyone.