Okay, I think I've got this figured out.  It's a problem in the distutils 
tests: the mechanism for saving and restoring environment variables in

Lib/distutils/tests/test_util.py

doesn't work:  after the line

        self.environ = os.environ

in the setUp method, self.environ and os.environ refer to the same object, 
so restoring using "os.environ = self.environ" doesn't do anything.

The attached patch (against py3k) fixes the problem for me;  trunk also 
appears to have this bug.

Assigning to Tarek.