This issue was first discovered by Mumbo Jumbo in his Honey block testing video: 

https://www.youtube.com/watch?v=SLqwJ2tmYNE

I noticed this and tried it out for myself. I noticed that if you try to push or spawn a Shulker onto a block it will teleport away. It also may teleport the Shulker inside of the block for a brief second, causing a lag spike.