Agreed. Cards that have completed and are "while in play" are CBN starting in the phase after they are completed.
However, I did have it ruled at Nats by a combination of Elders that if every time he enters battle, he reactivates, and therefore the protection ends and must be reactivated. If it is negated at that point, there is no more protection. At that point, the ability was not complete in a previous phase (as it reactivates), and can be negated in that battle.