It looks like this may be the symptom of a buglet in Thread.join:

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ERROR: test_communicate_timeout (test.test_subprocess.ProcessTestCase)
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Traceback (most recent call last):
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\test\test_subprocess.py", line 672, in test_communicate_timeout
    timeout=0.3)
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\unittest\case.py", line 689, in assertRaises
    return context.handle('assertRaises', callableObj, args, kwargs)
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\unittest\case.py", line 158, in handle
    callable_obj(*args, **kwargs)
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\subprocess.py", line 947, in communicate
    stdout, stderr = self._communicate(input, endtime, timeout)
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\subprocess.py", line 1193, in _communicate
    self.stdout_thread.join(self._remaining_time(endtime))
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\threading.py", line 1062, in join
    self._wait_for_tstate_lock(timeout=timeout)
  File "E:\home\cpython\buildslave\x86\3.x.snakebite-win2k8r2sp1-x86\build\lib\threading.py", line 1074, in _wait_for_tstate_lock
    elif lock.acquire(block, timeout):
ValueError: timeout value must be strictly positive