That didn't cross my mind, the jet washer did though. But looking closely it looks like some sort of paint reaction. My old Z3MC had a similar problem with laquer peeling from te bonnet. BMW eventually agreed to repaint it. A year later it did exactly the same, in the same spot.
Your not the only one to suffer from this as I was jsut reading a thread over a bimmerfest.com where a guy was having the same problem. I had to have the rear bumper on my car repainted not even two months after picking up the car. The paint on the rear bumper around the diffuser jsut simply peeled off. It was all covered under warranty but it really shouldn't have happened in the first place
Good news the stealer phoned today and confirmed it will be fixed as a warranty claim. They needed to make sure it hadn't been painted after leaving the factory. This has now been confirmed. Stealer was surprisingly good considering the service dept are pants. The manager said as the front end is plastic there can sometimes be a problem with a release agent in the plastic from the mould, sometimes in recessed areas the panel might not be prepared properly and due to the release agent the paint cannot key to the plastic properly. Thus my peeling issue. Anyway happy days again.