Very poor firmware in cheap Hamilton Beach microwave 

I had this problem with my microwave too. However it was a development rather than a bug. The door actually has 2 or 3 switches for keeping stuff on and off when the door is open. One will interrupt the carousel and the cooling fan, one turns on the light and a third turns off the magnetron. In my unit, one is located at the top and the others are located at the bottom. I had one that the switch itself had started to shift out of position and wouldn't make contact. I would experience the same phenomenon as you but it was after i had run the unit. Sometimes I wouldn't even have to open the door and it would keep going, even though the timer had gone off. Once I opened it up, I just re-positioned the switch, made sure the others were making good contact and were in position, and I was good to go. I would open this one up and see if that is the same case.

All microwave ovens do that cheap ones they all do it. its what the microwave dose

0:19

This is a older model of the microwave, we have a newer model that fixes the door issue. And it barely does it.

I had this problem with a hiar branded microwave and it was quite annoying

Maybe something is wrong with your microwave

Lol

Gf

Но

Mjj