Index: django/db/models/fields/related.py
===================================================================
--- django/db/models/fields/related.py	(revision 11208)
+++ django/db/models/fields/related.py	(working copy)
@@ -743,6 +743,10 @@
         cls._meta.duplicate_targets[self.column] = (target, "o2m")
 
     def contribute_to_related_class(self, cls, related):
+        try:
+            del(cls._meta._related_objects_cache)
+        except AttributeError:
+            pass
         setattr(cls, related.get_accessor_name(), ForeignRelatedObjectsDescriptor(related))
 
     def formfield(self, **kwargs):
@@ -782,6 +786,10 @@
         super(OneToOneField, self).__init__(to, to_field, OneToOneRel, **kwargs)
 
     def contribute_to_related_class(self, cls, related):
+        try:
+            del(cls._meta._related_objects_cache)
+        except AttributeError:
+            pass
         setattr(cls, related.get_accessor_name(),
                 SingleRelatedObjectDescriptor(related))
 
@@ -948,6 +956,10 @@
     def contribute_to_related_class(self, cls, related):
         # m2m relations to self do not have a ManyRelatedObjectsDescriptor,
         # as it would be redundant - unless the field is non-symmetrical.
+        try:
+            del(cls._meta._related_many_to_many_cache)
+        except AttributeError:
+            pass
         if related.model != related.parent_model or not self.rel.symmetrical:
             # Add the descriptor for the m2m relation
             setattr(cls, related.get_accessor_name(), ManyRelatedObjectsDescriptor(related))