piston stays powered

this is how i found it: i had a piston facing up, i put a redstone block on top. nothing. then, i put a block beside the base of the piston, and i put a redstone dust on top of that. the piston should extend. the you can break the redstone dust + the block it was on. the piston stays extended. this also works if you have 2 redstone blocks on top of the piston. then all you have to do is put a block (i used stone) beside the piston base and voila. the piston extends!