Start of by placing a block with redstone on it. Then place another block diagonally (left one block, up one block/right one block, up one block) and place redstone on it. Finally, place a piston on top of the first redstone you just placed. You will see that the texture of the connection of the two redstone is shifted some pixels away.
EDIT by [MCPE Helper] Zeb: It should be noted that functionally/server-side, the piston cuts off the wire, and the dust below the piston will power adjacent components like a normal plus-shaped dust (you can verify this by placing a redstone torch underneath the block the dust-that's-under-the-piston is placed on). The bug is that visually, the connected-upwards side texture appears, even though the dust isn't actually connected to anything. Also note that the piston cutting off redstone wire is intended - see