This bug report is a parity issue. The shulker opens into blocks when unable to teleport.

Steps to Reproduce
1. Place a block high enough in the air that the shulker cannot teleport to any other blocks in the area.
2. Cover all sides of the block except the top with buttons.
3. Place a block above the current block with one block of air between.
4. Cover all sides of that block except the bottom with buttons.
5. Spawn a shulker on the top face of the bottom block and observe for a few seconds.

Expected Results:
The shulker should have been unable to open into a block.

Observed Results:
The shulker continues to open, clipping into the block in the path of its shell opening.