Django - why are model attributes left updated when `not form.is_valid()`?

When using a model form:

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>>> honest_man.name
u'Abe Lincoln'
>>> form = PersonForm({'name': u'Barack'}, instance=honest_man)
>>> if form.is_valid():
...     print('Yay!')
...     bankster = form.save()
... else:
...     print('Uh Oh :(')
...
Uh Oh :(
>>> honest_man.name  # So, we'll just check to be sure nothing changed
u'Barack'
>>> # Oh no, our instance has been corrupted. Now I have to query for it to get
>>> # a clean version without the changes the form made.
>>> honest_man = Person.objects.get(name=u'Abe Lincoln')
>>> # Wasted query because I still need the instance

Is there a way to avoid this (I'm using Django 1.3)?

---

No, this can't be avoided in 1.3 because of model validation. After cleaning of form fields ModelForm populates instance's fields with cleaned data and calls instance.clean_fields() and instance.clean() methods.