WST3501 Problem. My WST3501 Microwave tends to turn itself on at random times. Sometimes when I

Question

My WST3501 Microwave tends to turn itself on at random times. Sometimes when I come back home the microwave would be on and working on its own. After the first incident, I've made it a habit to unplug the microwave whenever I go out.A strange thing happens whenever I plug in the microwave. As soon as I plug it in, the microwave begins to run as if it was heating something. If I open the door, it stops. But as soon as I close the door, the microwave keeps on running again, and it won't respond when I press either the "STOP" or any other buttons on the touchpad.I have to wait a while before the microwave starts functioning normally again---"normal" meaning that it will not spontaneously start running when I close the door.Does anybody know what is wrong my microwave?