I just ran into this issue in the logging module using 2.7. Here's the TB in
case it sheds any light on the issue

Traceback (most recent call last):
  File "./crawler.py", line 531, in <module>
    main(argv[1:]1:)
  File "./crawler.py", line 522, in main
    MCP(config).run()
  File "./crawler.py", line 332, in run
    self.reaper()
  File "./crawler.py", line 359, in reaper
    logging.debug('MCP process alive: %s', state)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 1600, in debug
    root.debug(msg, *args, **kwargs)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 1120, in debug
    self._log(DEBUG, msg, args, **kwargs)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 1250, in _log
    self.handle(record)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 1260, in handle
    self.callHandlers(record)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 1300, in callHandlers
    hdlr.handle(record)
  File "/usr/local/lib/python2.7/logging/__init__.py", line 746, in handle
    self.release()
  File "/usr/local/lib/python2.7/logging/__init__.py", line 700, in release
    self.lock.release()
  File "/usr/local/lib/python2.7/threading.py", line 147, in release
    self.__block.release()
thread.error: release unlocked lock

Since I'm not using threads, getting thread errors was a little bit of
a surprise. I guess trying to make the logging module thread safe
added a potential bug.