I don't know if this is a bug. But the poison potions (the poison effect in general) kills the player because the hearts of the head and torso go down to zero. (The death is often very fast and the time to react with a bucket of milk, it is already too late, provided you have milk on you).
Witches become the worst enemy of the game. It's as if the poison effect is replaced by the wither effect (it can kill in vanilla).

If this is intended, is it possible to have an option to disable this feature?

Yeah it should be fixed

Is this fixed? it just says "Closed"

Definitly a bug. Poison should behave like drowned damage and damage your non-critical parts first...

Thanks for confirmation.