about one week!
if you need fix now you can backup the file /components/com_users/models/registration.php and edit with this:

at line 101 replace this
$data['username'],
with
$data['email'],

at line 164 replace this
$data['username']
with
$data['email']

at line 416 replace this
$data['username'],
with
$data['email'],

at line 428 replace this
$data['username']
with
$data['email']

at line 453 replace this
$data['username'],
with
$data['email'],

at line 465 replace this
$data['username']
with
$data['email']

Attention: registration.php is a Joomla core file. BACKUP before edit. When we will release the new version you can restore the original file.