Shulkers can cause unpredictable End spawning

When Shulkers are present in The End spawning platform area, the player seems to spawn at a random location in The End upon entering. This only seems to happen in worlds where the spawning platform is enclosed inside the End Stone.

Steps to replicate:
1. Create a world with the seed 985175
2. Type "/setblock ~ ~ ~ end_portal"
3. Without moving, summon four Shulkers around the spawn position in The End. Place a solid block above each Shulker.
4. Leave The End (e.g. type "/kill")
5. Re-enter The End. You will sometimes spawn in a different location than the platform.