Gray cowl clearing bounty but NOT aggro.

[Quevik]

So i acquired the gray cowl of nocturnal from the AE CC. I wanted to test to see if it clears bounties like it did in oblivion. I equipped the gray cowl with 0 bounty, went on a murder spree in riften and accumulated 15000 bounty. Afterwards I left and unequipped the cowl out of sight of everyone.

My bounty was cleared (Stats sheet said 0 bounty in riften). However, when i returned the guards became hostile to me. Is there a something i am missing or is the cowl bugged?