I've no involvement with the programme, but I'd guess it may be that you term "desintegrating" maybe a little OTT. It could well be that the blades/RAT distort or damage above 320kn so that they can't be re-used? Frankly not a consideration in a real deployment, but something that you can really live without in training or routine air-testing.
As I said, pure guesswork, but it would be reasonably consistent with normal airworthiness (structural certification) practice.
G