Me ? Rant ? I would call it constructive criticism, however having had a look through the Manual, apart from all the beeps warning you of this that and the other including the end of the earth I could find nothing to indicate exactly what does switch the elements on so using a bit of intuition I would say there are multiple ways in which they may activate:-
Heated rear screen switch- if this is on then odds are that the temperature is low enough to warrant it.
Interior heater switch is set to on then odds are it's either steamy or frosty enough to require it
Sensors for outside ambient temperature are preset so that at a certain temperature it activates
Heated seats are activated because if it's cold enough for your bum then the screen will warrant clearing as well.
They are always on !
Cameras in the screen pod are indicating they are obscured so activate the elements.
All of the above and some we just don't know about
You know Mazda, if there's a way of making it complicated or as some will say looking for all eventualities for perfection
Question answered
? or have I confused the situation with my rant
( Oops, sorry constructive critique
)