If you shoot a shulker with an arrow when it peeks out, the block disguise dissapears

What I expected to happen was the shulker would disapear
Describe what you thought should happen here

What actually happened was the block disguise on the shulker dissapeared

Steps to Reproduce:
1. Use a bow and invisibility arrow
2. Wait until the shulker opens the block
3. shoot him when the block is still open
4. the block will dissapear and the head will remain