LibMemcached crash php-fpm

Question

I have PHP:

root@15048:/# php -v

PHP 7.0.3-1~dotdeb+8.1 (cli) ( NTS ) Copyright (c) 1997-2016 The PHP Group Zend Engine v3.0.0, Copyright (c) 1998-2016 Zend Technologies with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies

With installed memcached library:

And I have wrote class for working with memcached:

public $cache;

public function __construct() {
    $this->cache = new Memcached();
    $this->cache->setOption(Memcached::OPT_LIBKETAMA_COMPATIBLE, true);
    if (!count($this->cache->getServerList())) {
        $this->cache->addServer('127.0.0.1', 11211);
    }
}

public function get( $key ) {
    return $this->cache->get( $key );
}

public function set( $key, $var, $time ) {
    /*if ( $this->cache->set( $key, $var, $time ) )
        return true;*/
    return false;
}

public function flush() {
    if ( $this->cache->flush() )
        return true;
    return false;
}

public function __destruct() {
    $this->cache->quit();
}

But when I uncomment "set" function, JUST uncomment, and NEVER call it, php crash...

I have tried memcached "add" function has same issue...

[26-Mar-2016 14:26:42] WARNING: [pool www] child 15541 exited on signal 11 (SIGSEGV) after 26.168556 seconds from start

[26-Mar-2016 14:26:42] NOTICE: [pool www] child 15566 started

[26-Mar-2016 14:26:42] WARNING: [pool www] child 15542 exited on signal 11 (SIGSEGV) after 10.321759 seconds from start

[26-Mar-2016 14:26:42] NOTICE: [pool www] child 15567 started

[26-Mar-2016 14:26:43] WARNING: [pool www] child 15567 exited on signal 11 (SIGSEGV) after 1.305421 seconds from start

[26-Mar-2016 14:26:43] NOTICE: [pool www] child 15578 started

[26-Mar-2016 14:26:44] WARNING: [pool www] child 15540 exited on signal 11 (SIGSEGV) after 28.413800 seconds from start

[26-Mar-2016 14:26:44] NOTICE: [pool www] child 15579 started