With the greatest respect Flying Bull, rumours, ground-bound (and probably uninformed and over-excitable) witnesses and the media do not a reliable story make.
I've little doubt Rob Davies will co-operate fully with the German authorities (and I presume the AAIB as the aircraft is UK registered?) and he will be as keen as any for the reason for incident to be explained. Mustang canopies have come off in flight before, and if a second aircraft was in formation with the P-51D, it might well have moved clear after seeing BBD shed parts.
Cheers
Treadders