Not really a bug as much as it is a feature of most displays. If you are displaying anything - even in one corner of the screen - then the whole screen is effectively 'on'. There are no selective zones that are switched off.I've only owned my QX60 for about two weeks and I'm still "learning" but what I've found seems like a small bug in the display. When you turn off the display completely at night the clock still displays and the screen does not completely turn off. If you disable the clock on the nav display the screen will turn off - as in it will completely go black which is preferable - although I would like the clock displayed when it goes back on. To me this seems like a bug in the software.
Trying doing this on your TV and you will notice something very similar.
This is one reason I always loved the analog clock in Infinitis. You did not have to leave the screen on.