Index: django/db/models/base.py
===================================================================
--- django/db/models/base.py	(révision 7543)
+++ django/db/models/base.py	(copie de travail)
@@ -291,6 +291,12 @@
             signal = False
 
         for parent, field in meta.parents.items():
+            # At this point, parent's primary key field may be unknown
+            # (for example, from administration form which doesn't fill
+            # this field). If so, fill it.
+            if getattr(self, parent._meta.pk.attname) is None and getattr(self, field.attname) is not None:
+                setattr(self, parent._meta.pk.attname, getattr(self, field.attname))
+
             self.save_base(raw, parent)
             setattr(self, field.attname, self._get_pk_val(parent._meta))