ValuesQuerySets (and subclasses) were inadvertently not caching their results.

        # QuerySet.clone() will also set up the _fields attribute with the

        # names of the model fields to select.

    def __iter__(self):

        return self.iterator()

    def iterator(self):

        self.query.trim_extra_select(self.extra_names)

        names = self.query.extra_select.keys() + self.field_names