Piston not retracting when it's arm is powered

What I expected to happen was...:
Piston retracting when unpowering even it's arm is powered.

What actually happened was...:
Piston didn't retracted unless unpowering it's arm

Steps to Reproduce:
1. Power on the piston.
2. Power on it's arm.
3. Power off The piston's base
4. The piston doesn't retract(bug).
5. Power off it's arm
6. The piston finnaly retract