The argparse docs refer to an example of how to add a mutually exclusive group to an argument group to add title/description to those arguments. However, when used in parents to subparsers the mutually exclusive group is left out of the argument group help text description.

This snippet code:

from argparse import ArgumentParser

parent_parser = ArgumentParser(add_help=False)
parent_parser.add_argument('--common')
parent_parser_group = parent_parser.add_argument_group('New Group', 'Description.')
parent_parser_group.add_argument('--non-mut')
meg = parent_parser_group.add_mutually_exclusive_group()
meg.add_argument('--mut1', dest='mut')
meg.add_argument('--mut2', dest='mut')

parser = ArgumentParser(description='The main parser.')
subparsers = parser.add_subparsers(dest='subcommand', required=True)

command1_parser = subparsers.add_parser('command1', parents=[parent_parser])
command1_parser.add_argument('--c1')

command2_parser = subparsers.add_parser('command2', parents=[parent_parser])
command2_parser.add_argument('--c2')

command1_parser.print_help()

Prints out

usage: argparse_debug.py command1 [-h] [--common COMMON] [--non-mut NON_MUT] [--mut1 MUT | --mut2 MUT] [--c1 C1]

options:
  -h, --help         show this help message and exit
  --common COMMON
  --mut1 MUT
  --mut2 MUT
  --c1 C1

New Group:
  Description.

  --non-mut NON_MUT

But I was expecting

usage: argparse_debug.py command1 [-h] [--common COMMON] [--non-mut NON_MUT] [--mut1 MUT | --mut2 MUT] [--c1 C1]

options:
  -h, --help         show this help message and exit
  --common COMMON
  --c1 C1

New Group:
  Description.

  --mut1 MUT
  --mut2 MUT
  --non-mut NON_MUT

Also note that parent_parser.print_help() has the expected behavior, so something is lost when set as a parent.

usage: argparse_debug.py [--common COMMON] [--non-mut NON_MUT] [--mut1 MUT | --mut2 MUT]

options:
  --common COMMON

New Group:
  Description.

  --non-mut NON_MUT
  --mut1 MUT
  --mut2 MUT

How can I get a common mutually exclusive group with its own title/description in the help message of a subcommand?