when you throw a throwing potion of instant damage or poison to a player with a armor with the protection enchantment, the potion damage will be reduced, that is fine with the instant damage potion but not with the poison potion, the damage of potions with no instant-action effect should not be reduced because the effect is "inside of the player" and the effect should be override the player armor.

when you drink a potion of intant damage and poison the damage is also reduced, how can this be possible?, if the player drink the potion, the potion should be override the armor enchantment.

for this reasons and more some players in multiplayer dont use the potions with negative effects to attack.

thanks for read, sorry for my bad english, i dont speak it xD

note: would a cool idea if mojang add some method to change the potion colors and effect description in survival and creative mode, that would be cool to "trolling" player telling them that the potion has a good effect and the truth is that the potion has a bad effect xD.