I don't have the time to go in game to see what the exact wording, but I assume that it says it ends if hit or take damage. I am not sure with the mechanics, but if it is "hit", then in the beta (not sure if still), people were avoiding buffs meaning that this could be an extension of this. If it says "damage", then the mechanics might see healing as "negative damage" (not that uncommon in games).
Correct me if I am wrong however we won't get a clear answer until Stardock/GPG employee replies.
Oh and to answer the initial question, I am guessing bug since it is only suppose to prevent from using in combat.
