When a piston is powered with a 0 redstone tick pulse (or a half redstone tick pulse, meaning it's powered for only 1 game tick but not a full redstone tick), it only gives a pulse at some occasions, as it can be seen in the screenshots.

To reproduce:
Make a monostable circuit (a sticky piston facing up with a block on top and a repeater pointing at the block), put a piston with a block on its head, next to the monostable circuit (as it can be seen in the screenshots), and power it.