I have a bob tail panda who came directly from a reputable breeder.  I
don't consider this a "defect", this makes Gus even more unique!  I asked
about the tail and was told that it may be a defect or at times the
mother in an over zealous grooming at birth may have accidently bitten it
off.  Uuuugh, either way the only effect it seems to have on him is that
he is not as balanced when standing on his hind legs...but can jump
higher due to the lower hind end weight!
[Posted in FML issue 3889]