Memcached engine passes too many parameters

I know the memcached (not memcache) is still considered alpha quality, but I thought I would give it a try on a testing site I have to give feedback . I'm using pressflow 6, maybe that's an issue. Here are the warnings.

warning: Memcached::add() expects at most 3 parameters, 4 given in /usr/local/www/pressflow-6/sites/all/modules/cacherouter/engines/memcached.php on line 192.
warning: Memcached::set() expects at most 3 parameters, 4 given in /usr/local/www/pressflow-6/sites/all/modules/cacherouter/engines/memcached.php on line 92.

My libmemcached version is 0.37 and here is my cache router configuration.

$conf['cache_inc'] = './sites/all/modules/cacherouter/cacherouter.inc';
$conf['cacherouter'] = array(
  'default' => array(
    'engine' => 'memcached',
    'servers' => array('127.0.0.1:11211'),
    'shared' => TRUE,
    'prefix' => 'prod',
    'static' => FALSE,
    'fast_cache' => TRUE,
  ),
);

Let me know if I can provide any more info or test anything. Thanks!