unittest + coverage + multiprocess error

test_dbus (__main__.DbusServerTest) ... ok

----------------------------------------------------------------------
Ran 1 test in 2.014s

OK
Traceback (most recent call last):
  File "/usr/lib/python3.4/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/usr/lib/python3/dist-packages/coverage/__main__.py", line 4, in <module>
    sys.exit(main())
  File "/usr/lib/python3/dist-packages/coverage/cmdline.py", line 721, in main
    status = CoverageScript().command_line(argv)
  File "/usr/lib/python3/dist-packages/coverage/cmdline.py", line 438, in command_line
    self.do_execute(options, args)
  File "/usr/lib/python3/dist-packages/coverage/cmdline.py", line 580, in do_execute
    self.coverage.stop()
  File "/usr/lib/python3/dist-packages/coverage/control.py", line 410, in stop
    self.collector.stop()
  File "/usr/lib/python3/dist-packages/coverage/collector.py", line 294, in stop
    assert self._collectors[-1] is self
AssertionError
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