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):
+        # Queries on related models will fill the _related_objects_cache, we
+        # need to clear it to make the new relation visible
+        if hasattr(cls._meta, '_related_objects_cache'):
+            del cls._meta._related_objects_cache
         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):
+        # Queries on related models will fill the _related_objects_cache, we
+        # need to clear it to make the new relation visible
+        if hasattr(cls._meta, '_related_objects_cache'):
+            del cls._meta._related_objects_cache
         setattr(cls, related.get_accessor_name(),
                 SingleRelatedObjectDescriptor(related))
 
@@ -946,6 +954,10 @@
         cls._meta.duplicate_targets[self.column] = (target, "m2m")
 
     def contribute_to_related_class(self, cls, related):
+        # Queries on related models will fill the _related_m2m_cache, we
+        # need to clear it to make the new relation visible
+        if hasattr(cls._meta, '_related_many_to_many_cache'):
+            del cls._meta._related_many_to_many_cache
         # m2m relations to self do not have a ManyRelatedObjectsDescriptor,
         # as it would be redundant - unless the field is non-symmetrical.
         if related.model != related.parent_model or not self.rel.symmetrical:
Index: tests/regressiontests/query_between_definitions/__init__.py
===================================================================
--- tests/regressiontests/query_between_definitions/__init__.py	(revision 0)
+++ tests/regressiontests/query_between_definitions/__init__.py	(revision 0)
@@ -0,0 +1 @@
+
Index: tests/regressiontests/query_between_definitions/models.py
===================================================================
--- tests/regressiontests/query_between_definitions/models.py	(revision 0)
+++ tests/regressiontests/query_between_definitions/models.py	(revision 0)
@@ -0,0 +1,29 @@
+"""
+Bug 11448: Querying a model fills the _related_*_cache, making relationships 
+added later invisible
+"""
+
+from django.db import models
+
+class City(models.Model):
+    name = models.CharField(max_length=50)
+    def __unicode__(self):
+        return self.name
+
+# We can't actually query as the table does not exist.
+# Next best thing is to manually call City._meta.init_name_map
+# City.objects.filter(name='Amsterdam')
+City._meta.init_name_map()
+
+class Street(models.Model):
+    city = models.ForeignKey(City)
+    name = models.CharField(max_length=50)
+    def __unicode__(self):
+        return self.name
+
+__test__  = {'API_TESTS':"""
+
+>>> City.objects.filter(street__name='Weteringschans')
+[]
+
+"""}