gistfile1.diff

 The first time you call ``is_valid()`` or access the ``errors`` attribute of a
 ``ModelForm`` triggers :ref:`form validation <form-and-field-validation>` as
-well as :ref:`model validation <validating-objects>`. This has the side-effect
-of cleaning the model you pass to the ``ModelForm`` constructor. For instance,
-calling ``is_valid()`` on your form will convert any date fields on your model
-to actual date objects. If form validation fails, only some of the updates
-may be applied. For this reason, you'll probably want to avoid reusing the
-model instance passed to the form, especially if validation fails.
+well as :ref:`model validation <validating-objects>`.
+
+.. warning::
+
+    The cleaning process modifies the model instance passed to the
+    ``ModelForm`` constructor in various ways. For instance any date fields on
+    the model is converted into actual date objects. Failed validation may
+    leave the underlying model instance in an inconsistent state and for this
+    reason it's not recommended to reuse it.