Not noticed the brake lights, but since I have had mine, I have done very little night driving, so will find out soon as the evenings get darker.
It doesn't surprise me if the car only applies the brake lights when actually slowing down, that makes sense, as they are only there to warn other drivers you are slowing down, it would also make sense if they didn't apply them whilst sat at traffic lights, or even used the rear sensors to know when there was traffic behind the car, and turned them off then, maybe that's wishful thinking?