libmemcached - recovered memcached server is not recognized by php memcached -

i start 2 memcached servers, write data both of them.

i take down 1 memcached server. can see remaining server gets new memcached writes.

after 2nd server recovered, php memcached not using 2nd server. here configs using. doing wrong ?

 $memcache = new memcached ( 'a_mem_pool' );     $ss = $memcache->getserverlist ();     if (empty ( $ss )) {         $memcache->setoption(memcached::opt_recv_timeout, 1000);         $memcache->setoption(memcached::opt_send_timeout, 1000);         $memcache->setoption(memcached::opt_tcp_nodelay, true);         $memcache->setoption(memcached::opt_server_failure_limit, 50);         $memcache->setoption(memcached::opt_connect_timeout, 500);         $memcache->setoption(memcached::opt_retry_timeout, 300);         $memcache->setoption(memcached::opt_distribution, memcached::distribution_consistent);         $memcache->setoption(memcached::opt_remove_failed_servers, true);         $memcache->setoption(memcached::opt_libketama_compatible, true);         $memcache->addserver ( 'localhost', 11211, 1 );         $memcache->addserver ( 'server2.localhost', 8000, 1 );     }