Knight of the Living Dead not taking damage

After the Zombie King converts a random zombie into a Knight of the Living Dead zombie, the damage mechanic is broken. I have, on many occasions, watched as a zombie was turned. Then, on my turn, I hit it with a Berry Blast which should do 2 damage to it but it only does 1 and sometimes none. I have also seen this same issue when I hit the zombie with Bluesberry where it does no damage at all. I realize that it will take one less point of damage but that is not happening. I have also combo'd Bluesberry with Sgt Strawberry and have seen no damage taken from Sgt Strawberry even though Bluesberry was able to deal 1 point of damage. 

Can someone get me a clearer picture on this point?

Thank you