Ticket #2262: django-db-models-manipulators.diff

django/db/models/manipulators.py

@@ -214 +214 @@
 
                         # Save many-to-many objects.
                         for f in related.opts.many_to_many:
-                            if child_follow.get(f.name, None) and not f.rel.edit_inline:
+                            if child_follow.get(f.name, None) and not f.rel.edit_inline and not (f.blank and not hasattr(new_rel_obj, 'set_%s' % f.name)):
                                 was_changed = getattr(new_rel_obj, 'set_%s' % f.name)(rel_new_data[f.attname])
                                 if self.change and was_changed:
                                     self.fields_changed.append('%s for %s "%s"' % (f.verbose_name, related.opts.verbose_name, new_rel_obj))