Instant Damge Bug

Which hostile mobs are you throwing these at? Undead mobs (eg zombies) get healed by instant damage potions, and get hurt by health potions.

Duplicate of MC-2047.

The Instant Damage Potion I and II dont works on:
Skeletons,
Zombies and Zombie Pigmens

Again as stated in your own duplicate, instant damage on undead mobs heals them, while instant health damages them! Working as intended!