I experienced the same thing today on the first flight. This was after changing to the HS 55's before even trying to fly it. In my case, it was not a subtle change. It went from 3 feet high to about 10 feet high with no input from me. The wind was blowing about 10 mph, so that may have had something to do with it. It was my first flight ever on any heli and hey, I didn't crash it! Flew until the batteries went almost dead. Gonna be a fun hobby, I can tell.