> "running an unqualified python and expecting a PATH search to pick up
> the same executable as the parent shell would is not supported and may
> produce unexpected results"

CreateProcessW finds "python.exe" in __APPDIR__ before it even searches PATH. I expect that some scripts depend on this when python.exe isn't in PATH, or when a different version is in PATH. If subprocess implements its own search, it can continue to prioritize the *effective* application directory, from dirname(sys.executable).