Wind charges can randomly start moving one tick late when damaged by projectiles

Background

Deflectible projectiles, for example wind charges, can be deflected when damaged by an entity. The resulting velocity of the deflectible projectile is in the direction the entity was facing at the moment of damage application.

As a side-effect of Minecraft’s damage system, if a damaging projectile with an owner is used to damage the deflectible projectiles, the wind charges move in the direction the owner of the damaging projectile is looking. This is intended behaviour and is commonly utilised when a bow is used to deflect ghast fireballs.

Issue

The aforementioned interaction is rendered unusable in most situations. When a damaging projectile damages wind charges or other deflectible projectiles, the deflectible projectile may begin moving either on the tick the collision occurs, or on the next tick, regardless of entity creation order. This introduces a large uncertainty in the position of the deflectible projectile.

Steps to reproduce

1. Obtain multiple stacked wind charges. For example, one can summon multiple minecraft:wind_charge_projectiles stacked onto the same position using commands.

2. Shoot the wind charges with an arrow, or let a mob such as a skeleton do this.

3. Run the command /execute as @e[type=wind_charge_projectile] at @s run tp @s ~ ~ ~ in chat to stop the wind charges.

Expected result

The wind charges always stop in the same position, as they got hit by the arrow at the same time.

Observed result

Sometimes, the wind charges separate into two groups. This indicates that some wind charges started moving later than others.

Note

While the steps to reproduce this bug involve stacking the deflectible projectile, this is not necessary. The projectiles were stacked to highlight the fact that an individual deflectible projectile could end up in either stack. The bug occurs with single projectiles, with the projectile either moving on the tick the collision occurs or on the next tick.