Horses, donkeys and mules can enter boats as babies and then grow up inside of it, despite their adult variants not being able to enter it

The bug

Horses, donkeys and mules can enter boats when they're babies. While inside of the boat, they can grow up, leading to adult horses in boats. As the hitbox of an adult horse is larger than that of a boat (see MC-89963), the boat can then only be entered from below.

To reproduce

1. Place a boat
2. Spawn a baby horse on top or next of it, so that it enters the boat
3. Feed the horse with haybales
   → An adult horse sits in the boat

Original description

I played with friends and found a mistake. If you put a little donkey in the boat, and he grows up, then you will not be able to break down or get into the boat without killing the donkey or flooding the boat.