Fascinating in that our GE microwave (still actively sold) has an undisclosed feature that if you lift the door, when fully closed, by no more than a few mm, the microwave will start. I noticed this when cleaning the enclosure with a rag and my hand ever so slightly lifted up the door from the bottom. I can see how a consumer could wedge a kitchen utensil or plate accidentally under the microwave causing it to start and continue to run. Zero logic protection.
Doesn't seem limited to GE Microwaves! My wife uses a cheap Kmart house-brand microwave for waxwork that does the exact same thing.
I have another in the kitchen (Panasonic NNCD997) that has an interlock system which blows the primary fuse if a) The door is open and b) The magnetron is currently active.
Unfortunately, with this model, the incandescent bulb dying kills the inverter PCB.
Edit: The service/repair manual[1] for the Panasonic is an interesting read, if anyone is interested
A few weeks ago I noticed my cheap Toshiba microwave does the same when the door button is partially pressed. Scary! I stood there holding it just right for a very long time to make sure it wouldn't heat a cup of water.
