Cold through the middle vents - hot through the outside ones - help!!

[scotsgogs]

Hi folks, 2006 A6 saloon with climate control. Has worked faultlessly until very recently. All works well with the cc and then after running the car for a period - lets say an hour or so, the CC goes mental - the middle vents continue to blow cold air - the outside ones (driver and passenger) blow really hot air (no change to the temperature settings). Bizarre thing is that is you turn down the cc temp control then the outside vents blow even hotter air!!

Any clues folks?

Thanks in advance.