Collision box of Shulker in boat or minecart too high

The bug

When a shulker enters a boat, its current collision is seemingly saved permanently, making it too high in some cases.

How to reproduce

1. Grab a boat
2. Spawn a shulker
3. Enter survival mode
4. Wait for the shulker to extend
5. Place the boat next to it, getting the shulker inside
6. Return to creative and fly on top of the shulker

Video