I believe the common way to use `commit=False` (as noted in [#17988]([https://code.djangoproject.com/ticket/1798)) is like this:

    instances = formset.save(commit=False)
    for instance in instances:
        instance.user = user
        instance.save()

not call `formset.save` a second time. The test just demonstrates that `commit=False` doesn't delete objects while `commit=True` does.