So, DJI claims "improper operation" (launching from moving platform, I guess I moved my hand a bit or the boat was swinging in the breeze), but they're making an exception and sending me replacement for free. Huge props to them for that!
And I...
@BossBob: somehow I don't think that's it. I've experienced drone ignoring full throttle just once - when it was doing emergency landing due to low battery. But it never drifted sideways while descending, unless commanded to. There were no errors...
I have flown hours from boats, sometimes even in motion without any problem until now. It could be defective unit, it could be some unexpected mistake on my side... I wouldn't rule out the purchase based on one data point.
Let's see what DJI does...
I would say it went ~ 1 meter, above me, not more. It not climbing as it is supposed to was the first indication something is wrong. Yes, it flew sideways ~ 10 meters with increasing speed and hit the water with motors still running and no error...