Just gonna mention it here because it hasn't been pointed out before, but a key reason for the altitude loss after departure was that the collective FTR was engaged whilst the ALTA was coupled, meaning that their initially selected V/S of 1000fpm was replaced by a 'standard' value of 100fpm. Therefore, as they were rocketing up with more than 100fpm, and with the cyclic FTR still engaged (apparently no human interaction with the collective at the point), the autopilot reduced collective position to attain the 100fpm V/S. Despite all the other reasons and possible contributory factors mentioned above, I still find it a shame that the collective FTR was activated for the few seconds that the AP was coupled. Had that not happened, it is entirely possible they would have gotten away with it. A real Swiss cheese event.