Like all other python libraries, posixpath.normpath has its test cases,
which specify what normpath is supposed to work.
See test_normpath() in Lib/test/test_posixpath.py.

siemer, would you add some test cases for this problem to test_posixpath.py?
I think it needs not just adding but also need to update existent cases.
That means it would break backwards-compatibility.

According to http://www.python.org/dev/intro/,
changing existing functionality "requires python- dev as a whole to agree to the change."

So the TODO list would be

1. Write test cases for this problem and post it to the patch manager
2. Discuss the changes on python-dev at python.org and get agreement
3. Write patch and post it to the patch manager
4. Get some reviews
5. Commit

Correct Me If I'm Wrong.