Bison,
You should not be hitting the "Sign in with FB" button again, but instead filling out the registration information and hitting the Next button.
I do not know why JomSocial is including the social network login buttons on this registration page, but I think it's very confusing and the buttons can be safely removed. In components/com_community/views/register/view.html.php starting around line 76, this block can be commented out:
if ($config->get('usejfbc')) {
if (class_exists('JFBCFactory')) {
$providers = JFBCFactory::getAllProviders();
foreach ($providers as $p) {
$fbHtml .= $p->loginButton();
}
}
}
Then if you proceed through the steps after hitting the Next button, you will see that the mapped profile fields are imported correctly from FB, and the users are created correctly in the backend (in JomSocial, JFBConnect UserMap and the Joomla Users section).
-Melissa