Try cleaning the inside of the windscreen in the vicinity of the misting sensor (black box that hangs off the rear view mirror). Probably also a good idea to remove dust and dirt from the sensor window itself. My suspicion is that when the system detects the windscreen misting up, it switches the air conditioning compressor back on, even though it may have been manually turned off.
The other factor may be the air quality sensor, which according to the facelift-model handbook, is sensitive enough to detect the 'smell of spirits' from the windscreen washer. I wonder what happens when it gets a blocked nose, so to speak. The air quality sensor turns recirculation on automatically, which in turn probably turns on the air conditioning compressor - to prevent the windows misting up...
I wonder how we ever managed with the crude manual controls such as in my FIAT Punto, where you had to turn the air conditioning on by pressing the fan switch, and you had to turn the fan up AND set the air distribution to demist the windscreen, what a chore. Previous to that, we had Uno heater controls that were basically full-heat or no-heat, or full-heat blended with a blast of fresh air. A generation before that, my 128 Coupe had the water valve that would easily get stuck in the 'on' position, since a Bowden cable pushed it off (basically, like pushing a rope uphill).
Life is just so much better now I have a misting sensor, an air quality sensor, dual-zone control (so the empty passenger's side doesn't have to be warmed as much as my side) and no appreciable airflow from the windscreen vents, only a whistle