It happened to me several times and I find it very annoying.
When I park the car waiting for someone out if I leave phone in the car when I reach my destination and I forget to turn it off, Waze will prevent the screen from turning off and will drain out my battery quickly.
My suggestion is that I'd Waze detects that I'm parking or not driving for over a minute or so, it should automatically suspend the navigation activity and enable screen shutdown and sleep until user starts driving again.