In editor_menu_main() after the connection was saved we do:

  con_tmp = nm_client_get_connection_by_uuid (nmc->client,
                                              nm_connection_get_uuid (connection));
  ...

  /* Replace local connection with the remote one to be sure they are equal.
   * This mitigates problems with plugins not preserving some properties or
   * adding ipv{4,6} settings when not present.
   */
  if (con_tmp) {
    gs_free char *s_name = NULL;

    if (menu_ctx.curr_setting)
      s_name = g_strdup (nm_setting_get_name (menu_ctx.curr_setting));

    /* Update settings in the local connection */
    nm_connection_replace_settings_from_connection (connection,
                                                    NM_CONNECTION (con_tmp));

This works under the assumption that after the Update2() D-Bus method
returns, the local NMRemoteConnection is already updated with the new
values. Indeed, the NMSettingsConnection on server first emits the
"Updated" signal and then returns to Update2().

However, the Updated signal doesn't include the setting values and so
libnm has to fire an asynchronous
nmdbus_settings_connection_call_get_setting() to fetch the new
settings. This terminates after the Update2() method returns and thus
the initial assumption is not respected. As a consequence, the
"working" copy of the connection in the editor is different from the
NMRemoteConnection and it's not possible to save it because it's
considered dirty.

At the moment I'm not sure how to fix this.

Fix at:

https://github.com/NetworkManager/NetworkManager/pull/244

Merged upstream as 8af4f76 and backported to nm-1-14.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://access.redhat.com/errata/RHBA-2019:2302