The Bug:

You cannot change your crouching state while standing on top of shulkers located at y = 63.

Steps to Reproduce:

1. Summon a shulker at your position at y = 63, by using the command provided below.

   /summon minecraft:shulker ~ 63 ~ {NoAI:1b}

2. Stand on top of the shulker and attempt to change your crouching state.
3. Take note as to whether or not you can change your crouching state while standing on top of shulkers located at y = 63.

Observed Behavior:

You cannot change your crouching state.

Expected Behavior:

You would be able to change your crouching state.