Put the summary of the bug you're having here

What I expected to happen was...:
I expected that the piston would be turned off

What actually happened was...:
But piston was turned on

Steps to Reproduce:
1. You should add some button one the wall
2. [2x Pistons] Place a redstone line to the piston
3. After clicking 20/100 times piston is powered out of "nowhere".