I found a bug if you make a wall with a piston and a button above the piston and redstone behind the button. If you press the button the piston will stay extended. If you do like break a block that is touching the piston it will extract. If you can fix this I would be happy. I made a video on this but didn't post it. Here's a link to the video:
https://www.mediafire.com/?rk1ztbmc4ben445