Eyes of Kirathas and Eyes of Blackwater share "Lore" status.
You can have one mask or the other but not both.
If you attack the faction associated with the mask you are wearing/storing, it will break the spell and either mask poofs.
It's a small loss, about 53pp with the faction I got.
Also, if you already have aggro from a previous fight and wander back, you might re-aggro and lose your mask.
Best to zone or camp out and come back if you are unsure.
So don't attack Blackwater residents while wearing/holding Eyes of Blackwater.
Or
Don't attack the Elddar while wearing/holding Eyes of Kirathas.