Shulker Glithes Out When Below Shulker Box

When I was experimenting with shulker hitboxes I tried to place a shulker box facing south on top of the shulker, and then the shulker should've teleported away.

It didn't though and when the shulker tried to open it's head it started to flicker in and out of the block, in the direction th shulker box was facing.

Steps To Reproduce:
1. Place a shulker on the ground.
2. Place a shulker box 1 block above the shulker, while facing north, south, east or west.
3. Get the shulker to open its shell.
4. See how the shulker flickers back and forth in the direction of the shulker box.