Good info. Thanks! It makes sense that rumplessness is a skeletal mutation. I noticed my pullet tends to get a lot of droppings stuck on her feathers. This, too, could be contributed to skeletal deformation. We also have a tail-less black manx cat that has the same problems as the chicken.Someone else asked me about a rumpless Cream Legbar that popped up in a line related to mine, so I did a little research. This is a very informative article with a section about rumpless genetics. The "accidental" rumpless condition appears to occur in 1/1000 chicks, and is not hereditary. I think this is what you are working with.
http://www.araucana.com/Rumplessness.htm
