how can i fix?

i have a 1996 vw golf convertible, just bought, and im unsure if the rear windows are supposed to work when ign is on. when i unlock the car all windows open, which is right, i put ign on and i can put all windows up by the switches. however if i want to open my rear windows when driving the switches dont work for them to go down but they do work to go up. how do i fix this?