You can place Shulker Boxes where you're standing (inside the player)

Simple bug: You can place Shulker Boxes inside of yourself. Just face down while standing on a solid block and try to place a Shulker Box. Instead of not being able to place it like it should, you can actually place the Shulker Box (even though the player gets immediately teleported above the box).

This also works if you're standing just near a wall, face the wall and try to place a Shulker Box on it. Also with ceilings.