My gas stove has four burners. The two right-hand burners spark/click continuously when their gas is turned on, even when lit; I've cleaned the electrodes, aligned with with the flame, etc. However, when *both* right-hand burners are turned on and lit, they stop clicking. As soon as one of the two burners is shut off, they begin clicking again. This behavior is not present for the left-hand burners, which operate normally.

Where's the defect: Igniter? Electrode? Wiring?