I was not aware of this and bought a Samsung washer and dryer set a few years ago. Noticed one day that the dryer would keep spinning after the cycle ended. Then noticed that it started spinning before I turned the dryer on. I quickly realized that it now spins any time the door is shut, even when off.

Looked online and this is apparently a known mechanical bug in several models due to cheap components. So I can either unplug it or keep the door open anytime it's not in use. Never buying another Samsung either.