'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
    form = CheeseForm({'name': 'Brie'})
    self.assertTrue(form.is_valid())
    obj = form.save()
    obj.name = 'Camembert'
    obj.full_clean()
