This is a stair glitch. This might be a duplicate of another Issue, but in this issue I might have found the step-by-step way to do this. Although this glitch does work, it does not always work, in which I am guessing it has to do with NORTH and SOUTH directions maybe. As you can see, when the stair block is pulled back by the piston, the other stair block connected to the others acts as if it is still connected to the stair block that has been pulled back by the sticky piston. A step-by-step tutorial is you set up stairs like so in a cornered off set-up. You make a sticky piston move back and fourth repeatedly and pushing a stair block into one end of the cornered off stairs. You place a block in-between the stair block that is being pushed foward and backward by the piston and will sometimes get what is shown in the third picture.