Problem of Phalcon incubator's Redis backend cache

My project with Phalcon incubator's Redis backend cache. But it has some problem. When I use native PHP's Redis class ,it works properly and it shows "Cannot connect to Redisd server" when use Redis backend cache:

    // Cache data for one day by default
    $frontCache = new Phalcon\Cache\Frontend\Data(array(
        'lifetime' => 86400 * 24
    ));

    // If the has redis enabled, use redis for cache
    if ($config->redis->enable) {
        $redis = new Redis();
        $redis->connect($config->redis->host, $config->redis->port);

        // It is work properly here
        $redis->set('love', 'foo');
        die();

        // But when I use Phalcon Incubator's Redis cache backend
        // It says "Cannot connect to Redisd server"
        $backRedis = new \Phalcon\Cache\Backend\Redis($frontCache, array(
            'redis' => $redis,
            'prefix' => 'wwp-cache-'
        ));

        $backRedis->save('love', 'foo');
        echo $backRedis->get('love');
        die();
    }

Does anybody know why?

I'm working on Phalcon 2.0