A piston is being powered when it isn't supposed to

I was building a 7 segment display and I found this bug where a piston is being powered when it's not supposed to be.In the video is how to do the bug.

 

  her is how to recreate the bug 1.place a block down and then pales a piston facing down in to the block then you will want to place a redstone torch on the side of the piston and then place a block above the torch and then place a piston on the side of that block  and then another piston somewhere else but close to the mishing and you should see that weird stuff start to happen.