juju.unit.tests.test_workflow.UnitRelationWorkflowTest.test_depart_hook_error non deterministic behavior

Have seen this fail a few times. Is it possible the event that causes the error just hasn't happened yet?

[FAIL]
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1039, in _inlineCallbacks
    result = g.send(result)
  File "/build/buildd/juju-0.5+bzr504/juju/unit/tests/test_workflow.py", line 981, in test_depart_hook_error
    error_output.getvalue(), (msg + error_msg + "\n"))
  File "/usr/lib/python2.7/dist-packages/twisted/trial/unittest.py", line 270, in assertEqual
    % (msg, pformat(first), pformat(second)))
twisted.trial.unittest.FailTest: not equal:
a = ''
b = "Depart hook error, ignoring: Error processing '/tmp/tmpmHCxR4/units/mysql-0/charm/hooks/app-relation-broken': exit code 1.\n"

juju.unit.tests.test_workflow.UnitRelationWorkflowTest.test_depart_hook_error