Diagnosis
The cooktop light has an automatic feature. It turns on based on ambient light sensed by a photocell, not motion.
How to Fix It
To disable the auto feature, press and hold the KITCHEN LIGHT button for 3 seconds. The light icon on the display will change from 'AUTO' to 'MANUAL'. In manual mode, you control it solely with the button.
If That Didn't Work
A faulty control board can send erratic signals to the light relay. If toggling the mode doesn't stop random activation, the board may need service.
Heads Up
The photocell is located on the underside of the microwave. Do not block it with tape or objects, as this can cause overheating of the control system.