No, I'm not using the Google code backport.

To be clear, I've tried testing this with two versions of multiprocessing:
- multiprocessing-from-trunk (r82645): I get these exceptions with ~40% frequency
- multiprocessing from Ubuntu 10.04 (version 0.70a1): No such exceptions observed

Out of curiosity, I did just try this with the processing library (version 0.52) on a 64-bit Debian Lenny box, and did not observe these exceptions.

Hope that's useful!