'Re-cleaning an instance that was added via a ModelForm should not raise
a pk uniqueness error.'

def test_regression_14234(self):

    class CheeseForm(ModelForm, ):
        class Meta:
            model = Cheese
            fields = u'__all__'
    form = CheeseForm({u'name': u'Brie'})
    self.assertTrue(form.is_valid())
    obj = form.save()
    obj.name = u'Camembert'
    obj.full_clean()
