Shulker doesn't stay on non-full/non-solid blocks

when I summon shulker with egg amd command on stain glass it alway teleport to another place!
The block that It will teleport when it on

• Stain Glass
• Iron Bar
• Any Stair
• Hopper
• Head (when no block around shulker)
• End Rod
• Shulker [Cannot I know]
• Anvil
• Flower Pot
• Click on flower pot
• Any Sapling
• ETC [I dont know]

But when It on end portal (half block) it nothing happen