Minor There was some changes in Memcached server 1.4.5, resulting 2nd optional parameter of "delete" function called "$expiration" became required. That parameter is however not required based on it's documentation on www.php.net website. Because of that we can't delete keys we can get some outdated cached data as a result.
Way we process memcached servers doesn't correctly process case, when connection should be made using unix sockets.