I updated the patch with a few unit tests:

euclid:trunk minge$ ./python.exe Lib/test/test_lib2to3.py

...

======================================================================
FAIL: test_replace (lib2to3.tests.test_pytree.TestNodes)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/minge/Research/Languages/python/trunk/Lib/lib2to3/tests/test_pytree.py", line 161, in test_replace
    self.assertEqual(l2.parent, n1)
AssertionError: None != Node(1000, [Leaf(100, 'foo'), Leaf(100, '+'), Leaf(100, 'bar')])

======================================================================
FAIL: test_replace_with_list (lib2to3.tests.test_pytree.TestNodes)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/minge/Research/Languages/python/trunk/Lib/lib2to3/tests/test_pytree.py", line 179, in test_replace_with_list
    self.assertEqual(l1.parent, n1)
AssertionError: None != Node(1000, [Leaf(100, 'foo'), Leaf(100, '+'), Leaf(100, 'baz'), Leaf(100, '*'), Leaf(100, '*'), Leaf(100, 'bar')])

----------------------------------------------------------------------
Ran 541 tests in 19.328s

FAILED (failures=2)

...

euclid:trunk minge$ patch -p0 < python.patch 
patching file Lib/lib2to3/pytree.py
Hunk #1 succeeded at 132 (offset 2 lines).
Hunk #2 succeeded at 151 (offset 2 lines).

euclid:trunk minge$ ./python.exe Lib/test/test_lib2to3.py

...

----------------------------------------------------------------------
Ran 541 tests in 19.642s

OK