order_by interaction with "brew" distribution of Python 2.7.5 introduces edge-case regression

[Preston Holmes]

This commit:

​https://github.com/django/django/commit/69597e5bcc89aadafd1b76abf7efab30ee0b8b1a

introduced a change that interacts with the OS X specific "brew" installation of Python 2.7.5 to result in a regression in one test.

FAIL: test_tickets_2076_7256 (regressiontests.queries.tests.Queries1Tests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/admin/Desktop/django/tests/regressiontests/queries/tests.py", line 437, in test_tickets_2076_7256
    ['<Item: one>', '<Item: two>', '<Item: one>', '<Item: two>', '<Item: four>']
  File "/Users/admin/Desktop/django/django/test/testcases.py", line 776, in assertQuerysetEqual
    return self.assertEqual(list(items), values)
AssertionError: Lists differ: [] != [u'<Item: one>', u'<Item: two>...
 
Second list contains 5 additional elements.
First extra element 0:
<Item: one>
 
- []
+ [u'<Item: one>',
+  u'<Item: two>',
+  u'<Item: one>',
+  u'<Item: two>',
+  u'<Item: four>']
 
----------------------------------------------------------------------
Ran 1 test in 0.033s
 
FAILED (failures=1)

This is limited only to this patched distribution of Python. Unfortunately this is a rather common version to be running on developer machines.

This gist shows this error on a clean machine with the brew version of 2.7.5, and the python.org binary install version of 2.7.5

​https://gist.github.com/ptone/0764601b524fb87a690d

The crux of the issue can be seen in this PDB session started from the failing test:

(Pdb) Item.objects.filter(tags__isnull=False)
[<Item: four>, <Item: one>, <Item: one>, <Item: two>, <Item: two>]
(Pdb) Item.objects.filter(tags__isnull=False).order_by('tags')
[]