GroupedQuerySelectMultipleField validator is broken

[superosku]

GroupedQuerySelectMultipleField field validator does not raise Not a valid choice ValidationError if it is called with extra data that does not appear in what the fields query or query_factory returns.

This happens because the field has following pre_validate method:

    def pre_validate(self, form):
        if self._invalid_formdata:
            from pdb import set_trace; set_trace()
            raise ValidationError(self.gettext('Not a valid choice'))
        elif self.data:
            obj_list = list(x[1] for x in self._get_object_list())
            for v in self.data:
                if v not in obj_list:
                    raise ValidationError(self.gettext('Not a valid choice'))

On the first line this method checks if self._invalid_formdata but _invalid_formdata is only set at when getting the data property. That property does not get called before 6th line of this method.

This causes the validation to success incorrectly.