We saw a failure case like this with a microwave in the workplace kitchen. It somehow got into a mode where it only turned on when the door opened. Needless to say we threw it out shortly after that was discovered. We didn't bother debugging it, but my guess is it was a hardware problem because the interlock should have obviously made it work the opposite of how it was and you'd hope that a software glitch couldn't get it into a mode like that!