4
Nope
userform.php is used for editing registered users or adding new users through the administration menu.
For registrations, only username, password, email and timezone are set.
But try this in kernel/user.php
line 95:
$this->initVar('umode', XOBJ_DTYPE_OTHER, null, false);
change to
$this->initVar('umode', XOBJ_DTYPE_OTHER, _FLAT, false);