We encountered a problem where piston's models were not being registered with admin before admin URLs were being formed.
This resulted in some of piston's admin pages not working.
Currently piston registers its models with admin in models.py. Had they been in an admin.py file autodiscover would have seen them and registered them before admin URLs were added to the urlconf.
We have a workaround for this now which is importing piston's models in our url conf but that is not ideal.