Several months ago Adsense began opening a second account for Youtube revenue, complete with independent payment threshold, for existing Adsense users. You may have seen the message...
You have a new YouTube payments account. Any unpaid YouTube earnings will be moved to your new account from your old one before the next disbursement.
The "new" account is accesible from your adsense dashboard and has automatically included your name, banking information and tax information. It also has a different pub ID. it is truly a 2nd Adsense account, for Youtube only. Automatically opening accounts with a person's name, tax information and banking details when they don't even create youtube content isn't cool with everyone.
So how do you close the 2nd youtube only adsense account without closing the main adsense account?