In SearchEngines.php:55 there is "3271" defined as a independant search engine
// 3271 'nmsearch.3721.com' => array('3271', 'p'), 'seek.3721.com' => array('3271', 'p'),
Well, as the url is 3721.com and not 3271.com, I guess the name was just a typo.
But as those urls are opening the yahoo search they should be moved there.
(In ) fixes #1383 - remove nmsearch.3721.com favicon; update the Yahoo! China referrer URLs (including those from 3721.com)