vBulletin only works with utf-8 when you use MySQLi otherwise the AJAX elements cause problems. So Classifieds are not compatible with vBulletin when you use utf-8 properly?
Since when is MySQLi not a MySQL database?
You gave a different answer in this thread about MySQLi...
Is PHP 5.x.x ok for PhotoPost?
What is needed to make Classifieds MySQLi compatible?