I purchased a Hamilton Beach microwave, model # P100N30ALS3B (manufacture date March 2012) around summer/autumn of 2012 (I'm not sure exactly what month). Around 3-4 months ago, while sitting in my living room, I heard the microwave start. No one else was home - my son was at school and my husband was at work, so I knew no one had been in the kitchen to start the microwave.
I went to investigate, and found the microwave was running. I opened the microwave door, and as expected, the microwave shut off. However, when I closed the door, it immediately started up again without me pressing any buttons. I opened the door again, and once more the microwave shut off. Yet again, I closed the door, and again it turned back on of its own accord. I had to unplug the microwave to get it to stop turning itself on. After plugging the microwave in again, all seemed normal.
This happened again a few days later, and has happened around 12-15 times in total since it first began. The last time it happened was approximately a week ago, but I have no doubt it wasn't the last time it will happen. We now have to leave the microwave unplugged at night, and while no one is at home, simply as a precaution because we don't know when the microwave will randomly turn itself on again.