Hi Rosewhite,
I too have experienced sudden misting up, but only when the temperature outside has been low single figures.
For everyday setting I suggest that you only have the AUTO light lit. This should help to keep the cabin low in humidity.
To check that the various motorised flaps are working correctly I suggest that you take the car for a run until the engine is at working temperature, then find somewhere safe to park up with the engine running. On the right hand side of the air con panel are three buttons arranged vertically for manually sending the air up, sideways or down. Starting with the just the AUTO light lit, press the top UP button. The auto light should go out and the UP light should be lit. You may briefly hear a faint whirring sound as the flaps adjust and with your hand you should feel air coming out of the windscreen vents. Increase the fan speed if necessary. After about thirty seconds press the AUTO button again and the air direction will revert to its original setting.
Spend a while pressing the middle button, wait thirty seconds, then back to AUTO, press the bottom button, wait thirty seconds, press the AUTO button. All this is doing is giving the motorised flaps a bit of a workout as they can get sluggish if not used often. It may help to set the temperature to MAX and the fan speed to MAX while doing this. Do this once a week or so.
Never have the recirculate button lit while trying to demist, but you may want to add it to the workout described above.
Hope this helps,
John.
PS Oh and make sure the inside of your windows are spotlessly clean.