Added protection against proxying swapped models.

django/db/models/base.py

@@ -108,6 +108,11 @@ class ModelBase(type):
 
         is_proxy = new_class._meta.proxy
 
+        # If the model is a proxy, ensure that the base class
+        # hasn't been swapped out.
+        if is_proxy and base_meta.swapped:
+            raise TypeError("%s cannot proxy the swapped model '%s'." % (name, base_meta.swapped))
+
         if getattr(new_class, '_default_manager', None):
             if not is_proxy:
                 # Multi-table inheritance doesn't inherit default manager from

docs/topics/auth.txt

@@ -1953,6 +1953,18 @@ control access of the User to admin content:
     the given app.
 
 
+Custom users and Proxy models
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+One limitation of custom User models is that installing a custom User model
+will break any proxy model extending :class:`~django.contrib.auth.models.User`.
+Proxy models must be based on a concrete base class; by defining a custom User
+model, you remove the ability of Django to reliably identify the base class.
+
+If your project uses proxy models, you must either modify the proxy to extend
+the User model that is currently in use in your project, or merge your proxy's
+behavior into your User subclass.
+
 A full example
 --------------