When an arrow hits an entity that is in its invulnerable state (when taking damage, an entity has 0.5 seconds where it is immune to all damage) the arrow itself dosen't deal damage, but it nonetheless applies it's tipped arrow effect to the entity it hit.
This can be replicated by summoning an iron golem, and with a regular bow, instant damage II arrows and a right click macro (even 3 cps is more than enough) and see how long it takes to kill compared to fully charged shots with the same bow and arrows.
This bug makes harming arrows almost work like stacked harming potions.
With crossbows its even more noticeable: use a multishot crossbow loaded with harming II arrows at point blank range; it will kill an iron golem in 2 shots and a fully armoured and gaped up player in only 1.
TL;DR : tipped arrows ignore damage cooldown when applying their effect
Note: this bug can also be replicated on mobile but it takes more time and effort
Linked issues
relates to 2
Comments 6
Can confirm for 1.10, 1.10.1, and 1.11. On windows 10.
This is an easy bug to see when shooting shulkers that are closed, the arrows could pass right thru them or bounce off of them, and the shulker can still take damage/die if you use harming arrows. Try with crossbows as well. Weird stuff.
I'm not even sure whether the damage cooldown exists for potion effects. For example, eating a pufferfish can cause you to take damage more than 2 times per second, and totally ignores the 0.5s damage cooldown which I assume is intentional.
The issue relating to this is my post. Even when a tipped arrow is blocked with a shield, the player still gets the affect.
An easier way to reproduce it is to use a player in creative or any player when the pvp gamerule is disabled. This can be exploited to get free effects in survival (disabling pvp is not a cheat)