The hitboxes of horses, donkeys, and mules are not adjusted when they rear

The Bug:

The hitboxes of horses, donkeys, and mules are not adjusted when they rear.

Steps to Reproduce:

1. Enable entity hitboxes by pressing "F3 + B".
2. Summon a horse, obtain a bow, and hold it in your hand.
3. Right-click on the horse to make it rear.
4. Take note as to whether or not the hitboxes of horses, donkeys, and mules are not adjusted when they rear.

Observed Behavior:

The hitboxes are not adjusted when they rear.

Expected Behavior:

The hitboxes would be adjusted when they rear.