Reloading the world causes glitchy piston head

When I reload this world, a piston gets glitched out and another one does not extend (even though it's getting power).

To reproduce:

Make a piston tape, like the one I made here. B=Block, < =Piston
..v
....BBBBB<
> BBBB
..............^
Put a redstone torch in front of each piston, one block below. When there is a block there, power some redstone to make the piston push. Now it should go in a loop. Restarting the world might sometimes cause the pistons to glitch out.