Yes, http://bugs.python.org/msg166175 does use 'parse_args' in the second call.  But I think things would be more flexible if we had a second function:

    def parse_???(self, args=None, namespace=None):
        args, argv = self.parse_intermixed_args(args, namespace)
        if argv:
            msg = _('unrecognized arguments: %s')
            self.error(msg % ' '.join(argv))
        return args

But then what would a be a good pair of names?

parse??? and parse_intermixed_args
versus
parse_intermixed_args and parse_known_intermixed_args
or
something else?