Snap, noticed the same problem on mine a few weeks ago when hand washing so I rang the dealer and it is been replaced under warranty on June the 6th. It looks as if the exterior finished is laminated/bonded onto another alloy material underneath and the bond has failed in this particular area and allowed it to lift and bubble, the outer material is so thin its like the aluminium foil you use to cook things in!!! Never had this problem on my 2 B6 saloons.