serialize can't read ubuntuone oops report

To reproduce:

In [1]: import bz2
In [2]: import oops_datedir_repo.serializer_rfc822
In [3]: oops_datedir_repo.serializer_rfc822.read(bz2.BZ2File('/tmp/29210-1368storage1120.oops.bz2'))
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)

/home/matsubara/devel/canonical/oops-tools/829460-typeerror-qsmmx/<ipython console> in <module>()

/home/matsubara/devel/canonical/oops-tools/trunk/eggs/oops_datedir_repo-0.0.3-py2.7.egg/oops_datedir_repo/serializer_rfc822.pyc in read(fp)
     79 username = msg.getheader('user')
     80 url = msg.getheader('url')
---> 81 duration = int(float(msg.getheader('duration', '-1')))
     82 informational = msg.getheader('informational')
     83 branch_nick = msg.getheader('branch')

ValueError: could not convert string to float: unknown

Oops file can be downloaded here:
https://bazaar.launchpad.net/~launchpad-pqm/oops-tools/trunk/view/head:/src/oopstools/oops/test/files/oops-sample/ubuntuone/2009-09-29/29210-1368storage1120.oops.bz2

Oops file logged duration with value 'unknown'.