I have memcache installed, and the UI turned on, and it generates statistics for get, set, etc. However it does not generate anything for session caching, and a call to dmemcache_get(session id, 'session') comes back empty.

Here are the applicable settings from settings.php

$conf['cache_inc'] = $_SERVER['cache_inc']; 'this is set elsewhere and contains the valid path
$conf['memcache.hash_strategy']="consistent";
if (isset($_SERVER['HTTP_USER_AGENT']) && !preg_match("/(?:cron\.php|install\.php)/", $_SERVER['REQUEST_URI'])) {
  if (isset($_SERVER['HTTP_HOST'])) {
      $conf += array(
          'cache_default_class' => 'MemCacheDrupal',
          'session_inc'      => './sites/all/modules/contrib/memcache/memcache-session.inc',
           'memcache_servers' => array(
                  'localhost:11211' => 'default',
                  'localhost:11215' => 'session',
                  'localhost:11216' => 'users',
                  ),
           'memcache_bins' => array(
                'cache' => 'default',
                'session' => 'session',
                'users' => 'users',
               ),
  );
  }