tomchristie/django-rest-framework — pull request #651 by fernandogrd (2013-02-11 22:27:46+00:00)
Title: DictWithMetadata.__getstate__ was never called (Fix for 645)

I think I just found out the problem, self.__class.__.__mro__ return a list of classes, not instances, the code used isinstance. So the method was never called.

There must be something done by other cache backends that python-memcached don't, to ensure data was pickled even if __getstate__ returns None.