Failing doctests in lp:zeitgeist

Revision 1384 made two doctests to fail,

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FAIL: Doctest: test-engine-extension.rst
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Traceback (most recent call last):
  File "/usr/lib/python2.6/doctest.py", line 2145, in runTest
    raise self.failureException(self.format_failure(new.getvalue()))
AssertionError: Failed doctest test for test-engine-extension.rst
  File "/media/devel/zeitgeist/trunk/test/test-engine-extension.rst", line 0

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File "/media/devel/zeitgeist/trunk/test/test-engine-extension.rst", line 64, in test-engine-extension.rst
Failed example:
    engine.extensions.get_engine() # doctest:+ELLIPSIS
Expected:
    <_zeitgeist.engine.main.ZeitgeistEngine instance at 0x...>
Got:
    <weakproxy at 0x19553c0 to instance at 0x17d0dd0>

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FAIL: testCreateEngine (engine-extension-test.TestExtensions)
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Traceback (most recent call last):
  File "/media/devel/zeitgeist/trunk/test/engine-extension-test.py", line 51, in testCreateEngine
    self.assertEqual(engine.extensions.return_engine(), engine)
AssertionError: <weakproxy at 0x1ddf2b8 to instance at 0x1dcdf80> != <_zeitgeist.engine.main.ZeitgeistEngine instance at 0x1dcdf80>

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Ran 79 tests in 45.998s

FAILED (failures=2)

I don't get why we are using wekref here? Does this fix any particular bug?