Intermitent tests failing on tarmac

The following failure happens every now and then:

[ERROR]
Traceback (most recent call last):
  File "/usr/lib/python2.7/dist-packages/twisted/internet/defer.py", line 1045, in _inlineCallbacks
    result = g.send(result)
  File "/mnt/tarmac/cache/ubuntuone-client/trunk/ubuntuone/syncdaemon/event_queue.py", line 231, in shutdown
    yield self.monitor.shutdown()
  File "/mnt/tarmac/cache/ubuntuone-client/trunk/ubuntuone/platform/filesystem_notifications/monitor/linux.py", line 204, in shutdown
    reactor.removeReader(self._inotify_reader_antr)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/_glibbase.py", line 231, in removeReader
    self._remove(reader, self._reads, self._writes, self.OUTFLAGS)
  File "/usr/lib/python2.7/dist-packages/twisted/internet/_glibbase.py", line 218, in _remove
    self._source_remove(self._sources[source])
exceptions.KeyError: <ubuntuone.platform.filesystem_notifications.monitor.linux.MyReader object at 0x7b1e190>

tests.syncdaemon.test_action_queue.TestZipQueue.test_zip_acquire_lock