Oh well, there are half-brother/half-sister matings going on in a breed with a huge gene pool not so far away to 'preserve the lines' - but the KC will still register them, kerCHING!
I thought that this sort of thing only went on in the Fens of East Anglia, obviously not!
Perhaps the owners (assuming that they're a couple) were closely related before their own nuptials. It would certainly explain it. What's fit for the goose, and all that!