The -m switch creates a new module object to execute the requested module, and then throws it away before returning control to the interpreter core.

This is incompatible with the -i command line switch (and its environment variable equivalent), and would also cause problems if any code executed while looking for the module to be executed (e.g. sitecustomize.py or package __init__ modules) grabbed a reference to the original __main__ module.

(Creating bug report because I don't think the quick fix I checked in to SVN is adequate, and it's taking me longer than I planned to roll the quick fix back and fix the problem properly)