lp.services.job.tests.test_retry_jobs_with_celery.TestRetryJobsViaCelery.test_jobs_with_retry_exceptions_are_queued_again fails intermittently/rarely in parallel tests

Tests from worker 11: http://pastebin.ubuntu.com/1018438/

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FAILURE: lp.services.job.tests.test_retry_jobs_with_celery.TestRetryJobsViaCelery.test_jobs_with_retry_exceptions_are_queued_again
worker ID: worker-11
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Traceback (most recent call last):
_StringException: librarian-log: {{{
2012-06-01 22:37:25+0530 [-] Log opened.
2012-06-01 22:37:25+0530 [-] twistd 11.1.0 (/usr/bin/python2.6 2.6.5) starting up.
2012-06-01 22:37:25+0530 [-] reactor class: twisted.internet.pollreactor.PollReactor.
2012-06-01 22:37:25+0530 [-] FileUploadFactory starting on 52769
2012-06-01 22:37:25+0530 [-] Starting factory <lp.services.librarianserver.libraryprotocol.FileUploadFactory instance at 0xafe53ac>
2012-06-01 22:37:25+0530 [-] Site starting on 36200
2012-06-01 22:37:25+0530 [-] Starting factory <twisted.web.server.Site instance at 0xafe50ac>
2012-06-01 22:37:25+0530 [-] FileUploadFactory starting on 49381
2012-06-01 22:37:25+0530 [-] Starting factory <lp.services.librarianserver.libraryprotocol.FileUploadFactory instance at 0xafac24c>
2012-06-01 22:37:25+0530 [-] Site starting on 46157
2012-06-01 22:37:25+0530 [-] Starting factory <twisted.web.server.Site instance at 0xafac06c>
2012-06-01 22:37:25+0530 [-] Not using upstream librarian
2012-06-01 22:37:25+0530 [-] daemon ready!
}}}

Traceback (most recent call last):
  File "/var/lib/buildbot/slaves/slave/lucid-db-devel/build/lib/lp/services/job/tests/test_retry_jobs_with_celery.py", line 126, in test_jobs_with_retry_exceptions_are_queued_again
    self.assertEqual(2, dbjob.attempt_count)
MismatchError: 2 != 0