What I expected to happen was...:
The powered rail to stay on top of the double extending pistons while retracting

What actually happened was...:
They stay on the piston when double extending but break during the retraction

Steps to Reproduce:
1. Make a double piston extender pointing upward with a powered rail on top
2. Extend the bottom piston, then the top piston
3. Retract the top piston, then the bottom piston