Undead mobs are not affected by regeneration

Said this before but had it filed as a duplicate mistakenly, so I'll say it again.

Health and damage potions have opposite effects on undead mobs. Thats fine. I understand this is not a bug.

But poison and regeneration potions have no effect on undead mobs.

They should have some effect. I don't care if it is positive or negative, but they should do something.