Weird a/c problem with reverse

[BrickMan]

Not sure if this is some bizzarre vw 'feature'

2005 polo 9n (non facelift) 1.2 12v twist (climatic ac)

Had it two weeks, and already regretting it, so many small problems cropping up Wonder if anyone can point me in the right dircetion on this one

driving in forward gears, no problem, works fine
driving in reverse gears, with a/c pump on or off, the system opens the recirculation flap, makes a racket then closes, then opens again, and continues the entire time the car is in the reverse gear, unti lth ignition is switched off or moved back into a forward gear.

It didn't do it when I first bought the car (2weeks ago) now it does it.
the garage has fitted a new multiplug to the end of the reverse lights switch on the gearbox as it had corroded and they didn't work.
this a/c recirc problem has occured since then, but they swear they haven't touched anything inside the car.

Anybody any suggestson? I've got a warrenty, but not exactly eager to let the bloke loose on it, he's already done paint damage.

[towcestervag]

they are designed to do this read your manual
when reverse gear selected the blower speeds up and blows out air to clear screens