unpack_highres_date doctest fails on Python 2.7

The bzrlib.timestamp.unpack_highres_date doctest outputs a the repr value of a float timestamp, and with Python 2.7 has two fewer digits than the test expects:

    Traceback (most recent call last):
      File "...\python-trunk\lib\doctest.py", line 2153, in runTest
        raise self.failureException(self.format_failure(new.getvalue()))
    AssertionError: Failed doctest test for bzrlib.timestamp.unpack_highres_date
      File ".\bzrlib\timestamp.py", line 66, in unpack_highres_date

    ----------------------------------------------------------------------
    File ".\bzrlib\timestamp.py", line 76, in bzrlib.timestamp.unpack_highres_date
    Failed example:
        unpack_highres_date('Thu 2005-06-30 12:38:52.350850105 -0500')
    Expected:
        (1120153132.3508501, -18000)
    Got:
        (1120153132.35085, -18000)

There have been some changes to float string formatting to make it output the shortest string for the range represented, which I suspect relates to this failure:
<http://bugs.python.org/issue1580>

However, as I can't reproduce this problem outside the doctest I'm uncertain that that is in fact the cause.