Glitch with shulker mob

Shulker opening its shell into a block.

What I thought would happen was...
That it wouldn't open since there was a block in the way but it did.

What was happening...
I spawned shulkers on the top of a jungle tree then they teleported
so I went down the tree and found one whos top was pointing to leaves
then it opened his head and boom only half the head and other side had a texture glitch.

How to get this to happen...
1. Spawn a shulker on a jungle tree (this is where I found it)
2. Get it to teleport
3. Make sure the top of him is cover by leaves
Then he should open his head... Half of it and make a glitchy shell texture.