On rare occassions, with no payloads or attachments to block the sensors, my drone will land, but it's motors won't shut down. It's like it doesn't know it has landed. Then, the motors kind of speed up and slow down and just keep doing that. I am able to turn them off, by taking off again and relanding the drone, but when it takes off with it's motors running at a higher than normal rate, the drone doesn't go straight up. It moves like a foot away from the take off point, creating a potential to hit something during the relaunch. It makes me nervous. Has anyone had this happen to them?