Basically, the pistons, in some cases, will "teleport" when they get unpowered, on a double extensor. Note that the pistons push the block properly.
Below there are 3 images, the first one is the contraption before getting powered, my expectation was that the bottom piston would pull the block, what didn't happen(Note that this would happen before the Redstone Update).
The second image are the pistons being powered.
The third image, is the bottom piston getting back. It should have pulled the block, what didn't happen, what happened instead, was that it got teleported and then pulled by the upper piston.
At the right, you can see a wool colored machine, which was a 100% working double extensor before the Redstone Update, now it happens the same thing; piston not pulling block.