in most of the cookers, the base of the pot acts as the thermostat....when the water in the pot dries up, the temperature of the base of the pot increases, and this increase in temperature is detected by the thermostat and the power goes to 'warming' . This means, when there is a lot of water in the pot, it will not change to warming, which happened when you were cooking corn. but when you cook rice, the water dries up fast and thus the signal goes to 'warming'. If you want to test this, try putting the cooker on with very little water in it.