User Name Registering
 

I've upgraded to vBulletin 3.8.2 about a few weeks ago, and I've noticed here on this forum, and on others, when registering for a new account, it'll tell you if the username is already taken once you tab over to the Password box. On the forum I host, it does not do that. Is there a setting for this somewhere, or do I need to fix something in one of my files?