Bob, it sounds like a recessive popping up. Maybe consider getting an outside bird or two? Either a separate group, or a couple of females to cross into your line (carefully). As a non-show breeder, I want good everything too, but am not totally reluctant to bring in new blood.
As an aside, I've had a small group of Belgian d'Uccles since 1992 or 1993, and do introduce outside stock sometimes. My gene pool is just too small! Once I got birds with wry tails from a 'SQ' breeder, and eliminated them fast! I think that if I hadn't added new genetics occasionally, the group would have failed completely.
Mary