The Book by Morley Jull explains the Rumpless Chickens starts on page #215 Poultry Breeding by Morley Jull. I believe this Book can also be viewed on the internet. There are three types of Rumpless in chickens and this with your male is no heredity and you could if you wanted breed him to a hen with a tail and get good young.I don't think it's common but there was someone else on the MCCUSA board talking about rumpless Marans so apparently it does happen.
This is a good poultry book to own. sells very cheap on abe books.