Mode switching and strange behavior

ArduCopter Copter 4.0
1

ArduCopter 4.0.3 and 4.0.4-dev, MP1.3.72.
I checked this in real flight (4.0.3) but you can reproduce in sitl.

  1. Enable AUTO (or any automatic mode);
  2. Move the transmitter’s throttle stick to zero;
  3. Set flight mode to STABILIZE;
  4. Set mode to AUTO again and… Mode is AUTO but throttle still at min value and copter still fall down!
  5. Move stick up and AP says “AUTO_ARMED”, “THRUST_LOST_CHECK”. Now copter can continue mission.
    Looks like AP decided to do an automatic takeoff in air.