As a part of a bigger circuit, I had to push redstoneblocks (from now on, rb) 3 blocks up. When you place rb on top of a piston (piston facing upwards), nothing happens. But when the piston extends, it wont retract. Also, if you have 2 pistons one by the other, both of them facing up, and you place rb on top of one, you can't place it on top of the 2nd piston without the 1st one extending.