lp.services.job.tests.test_runner.TestTwistedJobRunner.test_timeout_short fails rarely/intermittently in parallel tests

I was unable to duplicate this locally with a --load-list of this and the previous tests in the layer, but here's the worker list if you want to give it a try yourself: http://pastebin.ubuntu.com/967608/. I was unable to find any reports in the syslog of an OOM error or other system-level explanation for why this might have happened. Since the instance was ephemeral, I could not look for application logs that might explain the error, because they were already gone.

======================================================================
FAILURE: lp.services.job.tests.test_runner.TestTwistedJobRunner.test_timeout_short
worker ID: worker-7
----------------------------------------------------------------------
Traceback (most recent call last):
_StringException: librarian-log: {{{
2012-05-05 00:05:54+0530 [-] Log opened.
2012-05-05 00:05:54+0530 [-] twistd 11.1.0 (/usr/bin/python2.6 2.6.5) starting up.
2012-05-05 00:05:54+0530 [-] reactor class: twisted.internet.pollreactor.PollReactor.
2012-05-05 00:05:55+0530 [-] FileUploadFactory starting on 43924
2012-05-05 00:05:55+0530 [-] Starting factory <lp.services.librarianserver.libraryprotocol.FileUploadFactory instance at 0xad2f3cc>
2012-05-05 00:05:55+0530 [-] Site starting on 56593
2012-05-05 00:05:55+0530 [-] Starting factory <twisted.web.server.Site instance at 0xad2f2cc>
2012-05-05 00:05:55+0530 [-] FileUploadFactory starting on 56049
2012-05-05 00:05:55+0530 [-] Starting factory <lp.services.librarianserver.libraryprotocol.FileUploadFactory instance at 0xad2f92c>
2012-05-05 00:05:55+0530 [-] Site starting on 46226
2012-05-05 00:05:55+0530 [-] Starting factory <twisted.web.server.Site instance at 0xad2fd6c>
2012-05-05 00:05:55+0530 [-] Not using upstream librarian
2012-05-05 00:05:55+0530 [-] daemon ready!
}}}

oops-0: {{{
Oops-Id: OOPS-20e22c8641b789c42c94239681446a7d
Exception-Type: ProcessTerminated
Exception-Value: A process has ended with a probable error condition: process ended with exit code 255.
Date: 2012-05-04T18:39:14.080063+00:00
Branch: devel
Revision: 15208
Duration: -1
Oops-Reporter: T

00000-00003@memcache-set MemcachedLayer__live_test
00083-00084@memcache-set MemcachedLayer__live_test
00185-00187@memcache-set MemcachedLayer__live_test
06118-06131@librarian-connection http://localhost:56593/93/filename-100193
06131-06131@librarian-read http://localhost:56593/93/filename-100193
06146-06152@librarian-connection http://localhost:56593/93/filename-100193
06153-06153@librarian-read http://localhost:56593/93/filename-100193
06161-06167@librarian-connection http://localhost:56593/93/filename-100193
06167-06167@librarian-read http://localhost:56593/93/filename-100193
22007-22016@librarian-connection http://localhost:56593/93/filename-100438
22017-22017@librarian-read http://localhost:56593/93/filename-100438
53935-53961@librarian-connection http://localhost:56593/103/bar_1.0.orig.tar.gz
53962-53963@librarian-read http://localhost:56593/103/bar_1.0.orig.tar.gz
53963-53963@librarian-read http://localhost:56593/103/bar_1.0.orig.tar.gz
61663-61673@librarian-connection http://localhost:56593/93/pmount.changes
61674-61674@librarian-read http://localhost:56593/93/pmount.changes
62153-62158@librarian-connection http://localhost:56593/93/pmount.changes
62159-62159@librarian-read http://localhost:56593/93/pmount.changes
62879-62884@librarian-connection http://localhost:56593/97/cdrkit.changes
62884-62884@librarian-read http://localhost:56593/97/cdrkit.changes
63685-63691@librarian-connection http://localhost:56593/98/pmount.changes
63691-63691@librarian-read http://localhost:56593/98/pmount.changes
177113-177114@memcache-set somekey
177114-177114@memcache-get somekey
177870-177880@librarian-connection http://localhost:56593/93/filename-102625
177881-177881@librarian-read http://localhost:56593/93/filename-102625
177883-177889@librarian-connection http://localhost:56593/94/filename-102651
177890-177890@librarian-read http://localhost:56593/94/filename-102651
178248-178254@librarian-connection http://localhost:56593/95/filename-102677
178254-178254@librarian-read http://localhost:56593/95/filename-102677
178257-178263@librarian-connection http://localhost:56593/94/filename-102651
178263-178263@librarian-read http://localhost:56593/94/filename-102651
184606-184617@librarian-connection http://localhost:56593/95/foo_1.dsc
184617-184617@librarian-read http://localhost:56593/95/foo_1.dsc
184618-184618@librarian-read http://localhost:56593/95/foo_1.dsc
185847-185859@librarian-connection http://localhost:56593/94/foo_1.0-2_source.changes
185859-185859@librarian-read http://localhost:56593/94/foo_1.0-2_source.changes
187117-187132@librarian-connection http://localhost:56593/63/hwsubmission1.xml
187133-187133@librarian-read http://localhost:56593/63/hwsubmission1.xml
187295-187301@librarian-connection http://localhost:56593/93/hwinfo.xml
187302-187302@librarian-read http://localhost:56593/93/hwinfo.xml
187413-187422@librarian-connection http://localhost:56593/94/hwinfo.xml
187423-187423@librarian-read http://localhost:56593/94/hwinfo.xml
187528-187534@librarian-connection http://localhost:56593/95/hwinfo.xml
187534-187534@librarian-read http://localhost:56593/95/hwinfo.xml

Traceback (most recent call last):
ProcessTerminated: A process has ended with a probable error condition: process ended with exit code 255.
}}}

Traceback (most recent call last):
  File "/var/lib/buildbot/slaves/slave/lucid-devel/build/lib/lp/services/job/tests/test_runner.py", line 593, in test_timeout_short
    (oops['type'], oops['value']))
MismatchError: !=:
reference = ('TimeoutError', 'Job ran too long.')
actual = ('ProcessTerminated',
 u'A process has ended with a probable error condition: process ended with exit code 255.')