php 5.4.6+apc cache error

<?php
class mySessionHandler{
        protected $mc;
        public function open() {
                $this->mc = new Memcached;
                $this->mc->addServer('172.16.3.82', 11214);
                $this->mc->setOption(Memcached::OPT_PREFIX_KEY, 'a_');
        }
        public function close() {
                unset($this->mc);
        }
        public function read($session_id) {
                return $this->mc->get($session_id);
        }
        public function write($session_id, $data) {
                return $this->mc->set($session_id, $data);
        }
        public function destroy($session_id) {
                return $this->mc->delete($session_id);
        }
        public function gc($maxlifetime) {
                return true;
        }
}

class mySessionHandlerS{
        static protected $mc;
        static public function open() {
                self::$mc = new Memcached;
                self::$mc->addServer('172.16.3.82', 11214);
                self::$mc->setOption(Memcached::OPT_PREFIX_KEY, 'a_');
        }
        static public function close() {
        #       unset(self::$mc);
        }
        static public function read($session_id) {
                return self::$mc->get($session_id);
        }
        static public function write($session_id, $data) {
                return self::$mc->set($session_id, $data);
        }
        static public function destroy($session_id) {
                return self::$mc->delete($session_id);
        }
        static public function gc($maxlifetime) {
                return true;
        }
}


ini_set('session.save_handler',   'user');

$classname = 'mySessionHandlerS';
session_set_save_handler(

                "{$classname}::open",
                "{$classname}::close",
                "{$classname}::read",
                "{$classname}::write",
                "{$classname}::destroy",
                "{$classname}::gc"

                );
/*
$handler  = new mySessionHandler;
session_set_save_handler(
                array($handler, 'open'),
                array($handler, 'close'),
                array($handler, 'read'),
                array($handler, 'write'),
                array($handler, 'destroy'),
                array($handler, 'gc')
                );
*/
session_start();
$_SESSION['a']++;


var_dump($_SESSION);