Whenever a command block spawns a piston next to any redstone signal, it loses its pushing animation. However, manually placed pistons and pistons spawned by player command don't have this problem. (As seen in piston.mp4)

Edit: Blocks pushed by command block pistons also don't have a proper pushing animation. Instead, they seem to teleport. This also applies to the player. (As seen in pistonblock.mp4)