I saw this happening on my 07 TI in the last few days also - coincides with warm weather and rain so the car was misting up. As far as I can tell from reading the manual, you can not stop this happening - the sensors have determined a part of the windscreen is misting up, therefore you will not be able to see and will crash - unless they turn on the AirCon and demist. Big brother in a car!!!!
Just another one of those weird Alfa quirks we all love.
Next time it happens, stop the car, get out, walk 10 yards away and then turn around and look at the car - all will then be forgiven!