Well, your skis naturally roll from behind on you to your car at high speed forward is somewhat disturbing. But considering that you have to be the owner of a Cayenne or Macan that has ever bought the Porsche ski bag, and then you have to use that thing, you're probably safe.
On the other hand If you have a ski bag with a Macan or Cayenne, you either have to: a) move your trip to the Alps or b) buy a roof rack. Not the end of the world. If you are one of those 95 unfortunate people, you can receive a note from your Porsche dealer shortly asking you to claim your new free replacement bag.