I was doing some wiring for a piston set up that moves sand. I had various pistons and redstone and repeaters. When I found that the sand wasn't moving how I wanted it to, that was when I thought something was wrong.

A piston powered with a repeater over it will be powered as if the repeater is redstone.

1. Place two pistons horizontally next to each other (Second pic)
2. Put sandstone over them (Third pic)
3. Put the torch, repeater and redstone on top of the sandstone (First pic)
3a. The one on the right is RdStn, Rptr, Torch.
3b. The one on the left is Rptr, RdStn, Torch.
4. I also demonstrated with wool and other piston setups (last two pics)

Red wool signifies a piston with just redstone directly over it. Black wool signifies that the piston has a repeater over it or it should otherwise be unpowered.