Index: Lib/argparse.py
===================================================================
--- Lib/argparse.py	(Revision 86681)
+++ Lib/argparse.py	(Arbeitskopie)
@@ -1481,6 +1481,7 @@
         self._defaults = container._defaults
         self._has_negative_number_optionals = \
             container._has_negative_number_optionals
+        self._mutually_exclusive_groups = container._mutually_exclusive_groups
 
     def _add_action(self, action):
         action = super(_ArgumentGroup, self)._add_action(action)