Zombies only fight back against players

Short Description: Zombies dont fight back when attacked by other entities than the Player

Longer Description: Im a modder and I first noticed this bug when I made a guard npc that attacks nearby creatures. Whenever it attacked a zombie it would never get hurt. I then went on testing this, but it also doesnt seem to attack a tamed wolf. Zombies not attacking my guard npc might not be considered a bug, though skeletons attack back just fine. The zombie not attacking the wolf is clearly a bug.