Mine's currently the same too, and will be looked at by the Citroen dealer when it goes for its service on its 2nd birthday...
I've got a feeling it's temperature-related on mine at least, but I could be completely wrong. Mine does stop if it's had a run then sat still for a few minutes - presumably when it's got warm after not having any air blown through it. It also stopped OK the other day when I was queueing in traffic, which supports my theory.
My thinking is that the thermostat's stuck partly open, so the warm water's going through the radiator all the time, whether it needs cooling or not. So if it's moving it will always be too cold due to the road speed airflow into the front, so it correctly decides not to stop. Normally, the thermostat should stay closed to keep the heat within the engine if it's not up to operating temperature, only opening once it's hot.
Is your temperature gauge below 90 (horizontal)? Mine is, by about 3-4mm and never gets any higher. I know this isn't an accurate measurement, but it's a hint that this could be the problem. My OBD system's on the way from China, so I can't check it accurately for myself until this arrives.
I'll update the other thread when I find out more after it goes in on the 31st of October.
Oh - welcome, by the way!