Menu cache does not invalidates properly.

This issue might be a duplicate, I can't really decide.

Reproducing the bug is very simple:

• install Drupal 7 and install Memcache properly. This is my settings.php:

$conf['cache_backends'][] = 'sites/all/modules/memcache/memcache.inc';
$conf['cache_default_class'] = 'MemCacheDrupal';
$conf['lock_inc'] = 'sites/all/modules/memcache/memcache-lock.inc';
$conf['memcache_key_prefix'] = 'playzin_';

• reload home page to populate the menu cache
• edit main menu's only menu item, change the title to something different than "Home"
• Check the home page, the menu item has not changed. After clearing the cache manually, the menu item updates properly.

System:
Ubuntu 10.04 LTS
PHP 5.3.2
php_memcache 3.0.4
Apache 2.2.14