The bug

When parrots ride on players' shoulders, they move downward when the player sneaks. If a non-parrot mob rides a player, though, their position does not adjust for sneaking.

Steps to reproduce:

• Install the attached behavior pack and apply it to a world.
• Summon a cat, then approach it. It should automatically ride the player.
• Sneak with the cat riding on you.

→ Its model does not adjust for the player sneaking, and remains stationary.