Though blocks aren't suppose to go through the height limit of Y=256 piston heads and opened shulker boxes are able to go through the Y=256. For the piston head, the hitbox gets cut off when trying to activate the piston near Y=256, only the body will have a hitbox. The shulker box however doesn't fully go through that Y level, probably intended if the shulker box on Java does the same as Bedrock.