Piston doesn't push.

Does not let you swap blocks back and forth with pistons.

Steps to Reproduce:

1. Recreate Redstone contraption. [Redstone repeater is set to one tick.]
2. Turn leaver on and off a few times.

Observed Results:
Piston doesn't push block.

Expected Results:
The fist piston should retract as the fist is pushing.

Screenshots/Videos attached:   

Notes: