During tesing of motor-off recovery at safe altitude (60meters), the quad fell stright down, - propellers were spinning backwards, and motors stalled, not being able to turn in right direction.
At much too low altitude, the quad rolled, making 2 of the motors able to spin up, but it was too late then.
-motors should be kept on at all time when the APM is armed, stopping motors is asking for dangerous situations..
I created a issue here: https://github.com/diydrones/ardupilot/issues/431
Feel free to support it.