Ford Focus LCD staying on when car locked?

I have just noticed that after locking my Ford Focus, the LCD and radio lights remain lit. I'm sure that they normally turn off.

The only reason I can think they might be on is that the temperature is 3 degrees, which means when the car is on the frost warning is showing. Could this be the reason that the LCD panel is remaining lit? How long might it stay on for?

(Can't see any explanation in the manual.)