I have been out and about this evening in my i30 1.6 CRDi and for most of the time the auto stop has been disabled. Previously this has been a sign that the DPF his being regenerated but the last regeneration was only 80 miles ago and the trip economy failed to show any increase in fuel consumption. Hence I doubt that the DPF had anything to do with it.
For the first time since I bought the car in April the frost warning light came on - with the temperature in the dash showing 4ºC. Can it be that Auto Stop is deactivated when the temperature is low.
Perhaps our friends in the colder Euro countries with a new i30 can help to shed some light on the matter.