There are several problems with the patch provided in msg156315
This description:
"Added patch so that only the first '--' is removed by an argparse.PARSE or argparse.REMAINDER argument."
should read
"Added patch so that only the first '--' is removed by arguments that are not argparse.PARSER or argparse.REMAINDER ."
The test that adds a third subparser with a nargs='...' argument does not test this change. It exercises both nargs types that are not affected by the change in argparse.py. As such older versions of argparse pass this test.
I thinking argparse.py change is correct (delete only the 1st '--'), though I'm not sure it addresses the concern of the original poster.