Shulker open and close hitbox is not updated, when they ride boat, minecart or mobs

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The following is based on decompiled version of Minecraft 1.9 using MCP 9.24 beta. All method and class names are the names used in the decompiled version.

The reason why this happens is because the method net.minecraft.entity.monster.EntityShulker.onUpdate() only updates the bounding box of the Shulker if the block position of it is not null. However, if the Shulker is riding another entity the block position is set to null. Another problem is that the EntityShulker class is not overriding the method net.minecraft.entity.Entity.setPosition(double, double, double), which is for example called for the riding entity when the ridden entity moves. This method sets the bounding box based on the height, which the EntityShulker class is not using.

Can confirm in 20w48a. You can use these commands to help reproduce this bug.

/summon boat ~ ~ ~ {Passengers:[{id:shulker}]}

/summon minecart ~ ~ ~ {Passengers:[{id:shulker}]}

Can confirm in 20w51a, however cannot in 21w03a. This issue has been fixed in 21w03a.