Just installed latest version of arducopter on my pixhawk quad x. In stabilize mode for my first flight. Take off and after a few seconds at about 5 feet above the ground it beeps and then flys up to about 50 feet off the ground. I drop the throttle to zero and it keeps going. Then some more beeps and it comes down and lands. Any ideas what I could be doing wrong? This is my first pixhawk build.