Win32 CreateProcess requires that the environment block be sorted alphabetically, case-insensitive. This isn't currently done by win32process, so subprocesses won't see all the environment vars in the dictionary. See the thread around http://mail.python.org/pipermail/python-dev/2004-October/049656.html
for a discussion of this, and how to solve it.
(This also affects the Popen class in the subprocess module, which takes an env argument and calls CreateProcess.)