If piston below configuration (initial configuration.jpg, by placing the pistons first, then the block and the Redstone block), if either the non-Redstone block or the second piston (second from the non-Redstone) breaks, the piston will be extended, and remain extended without any way to retract. Now, in the initial configuration, if there were Redstone dust placed after the placement of the Redstone-block on either or of the pistons, it will cause the first piston to extend and get stuck. If there were Redstone dust were place on top of the second piston, before the placement of the Redstone-block, then broken after the placement of the Redston-block, the first piston will be stuck extended.