When sneaking while standing on a shulker, the sneaking animation does not play

Put the summary of the bug you're having here

What I expected to happen was...:
I thought I could crouch if I press shift when I stand on a shulker.

What actually happened was...:
I couldn't crouch and I was stuck in crouching if I crouched on the shulker.

Steps to Reproduce:
1. Sneak on a shulker
2. When you stand on top of it release the shift button