I don't know, I've seen both sides of that coin. I've had enemies that just commit suicide for no reason, and I've also had a group of zombies use chains of pain on my character with broken armor, and then they grouped up and wacked their zombie constantly. Since they were dealing poison damage, and healing the zombie, it wouldn't kill him. However, the damage DID transition over to the other character, every time they healed their own, it damaged mine.