A map should show by green marker, if there are copies of it and there they are. If you hang a map in the nether, it shows wrong green copy positions on the map. On the screenshot you see four green marker, because I put four maps in the nether near the positions  x0, y61, z0; x100, y61, z0; x0, y61, z100 and x100, y61, z100. At the shown land there are no copies hanging around.