Put the summary of the bug you're having here

*What I expected to happen was that the three sand get pushed up and stay
Describe what you thought should happen here

*What actually happened was, that one sand glitched under the third piston,destroying the mechanisme
Describe what happened here

Steps to Reproduce:
1. try to build a three piston door (to up)
2. place three sand on it and power it
3. deactivate it, and see the glitch
(the two lowest pics show how the pistons are connected)