The documentation of CREATE_NEW_CONSOLE at http://docs.python.org/3/library/subprocess.html#subprocess.CREATE_NEW_CONSOLE states:

    This flag is always set when Popen is created with shell=True.

This does not fit the code which does

    if (_subprocess.GetVersion() >= 0x80000000 or os.path.basename(comspec).lower() == "command.com"):
        # Win9x, or using command.com on NT. We need to
        creationflags |= _subprocess.CREATE_NEW_CONSOLE

So the statement is only true on very old versions on Windows. I suggest to fix the documentation (patch attached) or to remove that obsolete hack (and drop support for Windows <= NT).