Thanks for the reply Steve.
I think you may have missed my point: the lights, when set to auto, don't ever go out (until the battery is flat ) even if I open and close the door and lock the car. Even in the most basic car there's usually a reminder buzzer that the lights are on when the key is taken out of the ignition or there is some time delay after locking the car before the lights are extinguished automatically. The 400h seems to have a deficiency in both departments, unless I'm mistaken or missing something. For a car with a 'fragile' 12V battery, inadvertently draining charge by allowing the lights to remain on seems to be a real shortcoming.
Nick
I know this is an old post... but does your RX have a headlight on warning buzzer? You wrote, "Even in the most basic car there's usually a reminder buzzer" < I agree, but I've not been able to confirm this.
Mine is an RX350 2010 model.