"virsh attach-interface [...] --config" does not work as documented

Issue

• The Parameter --config of virsh attach-interface does not work as expected.

• The manpage states:

  If --config is specified, affect the next boot of a persistent guest.
  

  But the although --config is specified the change gets applied immediately

• virsh help attach-interface tells:

  --config         affect next boot
  

  But although --config is specified, the interface gets added immediately.