Problem:
You will get stuck inside a piston when moved upward by that piston and above you is a block.
Reproduce:
1. Construct a double piston extender without the second block retraction (If you do it, the block will push you out) (There is also a version below)
2. Stand on the second piston and put a block on top of your head
3. Flick the lever and you will get stuck