xmppframework/contrib/xmpp_node_muc/xmpp_node_muc.module: 

 function xmpp_node_muc_create_muc(....) {

...
      xmppframework_configure_muc($name, $service, $server, 'members_only', true);

but in the implementation function:

xmppframework/contrib/xmpp_api/xmpp_api.internal.inc:

 function xmpp_api_configure_muc($name, $service, $server, $option, $value, $conn = NULL) {

...
 // have pre-determined options that we want to set the muc as i.e. title, persistent etc
  $options = _xmpp_api_muc_config_options($value);

Hence, $value is supposed to be room title, but is being set to boolean TRUE.

Also, $option = 'members_only' is never used.