I don't believe this is an interpreter or stdlib problem. See this post from September last year:
http://plumberjack.blogspot.com/2010/09/using-logging-with-multiprocessing.html
which shows how to use multiprocessing and logging together with rotating logs. The post includes the code for a complete working script which runs fine with Python 2.6 on Windows and Linux, but which I can't test on Mac OS X/Python 2.6 as I have no access to a Snow Leopard system.
You're welcome to run that script on your system and update this issue with your results - so I'm marking as "invalid" for now (as I don't believe there's a valid Python issue) and "pending" awaiting your feedback. If I don't hear from you in the next week or so, I'll close this issue.