Auto switching on of heated screens ????

Hi all,
Came across a strange one over the last 2 days.

As we all know it's been cold overnight the last few days, so 1st thing I start the S and turn on the heated front screen, rear window and heated seat. These stay on until they switch themselves off. 

Nothing unusual about that I heard you say but the last 2 days then I leave work to go home and on starting the engine the heated front and rear window have automatically switched themselves on (the external temp was above 9c).

This has never happened before, I always have to turn them on if needed (not that they are needed then temp is above 5c anyway).

The touch screen/ sat nav was retrofitted from my last S so I've been using it for over 4 years now.

Any ideas?

Thanks.