blinking repeater

i was building an adder that had an AND thing with an upside-down sticky piston with an iron block at the end, and a repeater going into where the iron block would be if the sticky piston was extended was extended, and a redstone wire coming out the other end, so current would only get to the last redstone wire if the piston extended and the repeater was getting power, but even if i cut off power to the repeater (but left the piston extended), the repeater started flashing like crazy :\