When You destroy a minecart that a shulker is riding in then the shulker will put itself on the block the rail is on, resulting in the shulker being inside a rail or the rail inside a shulker.

How to recreate:

1) Spawn a shulker

2) Have a minecart on a rail leading up to the shulker

3) Push the minecart into the shulker, the shulker will ride the minecart

4) push the shulker onto the track and destroy the minecart

Expected results:

The shulker dismounts then teleport to another block (Maybe)