Pitts, the one in a billion flight hours is of course a calculated probability, as it is for virtually all things to do with certification.
Clearly the false alarm rate is unacceptable, but fortunately we now know why its doing it a minor change to operational procedures will avoid it, although it would have been better if it hadn't done it in the first place!
Pablo, 2 thou depth doesn't sound a lot but in the context of a machined mirror finish, its obvious to the naked eye.