This issue isn't specific to Windows. It's a bug in shutil._basename:


    def _basename(path):
        # A basename() variant which first strips the trailing slash, if present.
        # Thus we always get the last component of the path, even for directories.
        sep = os.path.sep + (os.path.altsep or '')
        return os.path.basename(path.rstrip(sep))

It should use `os.fspath(path)` to get the path as a string.