The Smarty modifier strip_unsafe_html calls String::stripUnsafeHtml, which uses HTMLPurifier according to the ‘allowed_html’ rules in config.inc.php. The configuration set in config.inc.php won’t show up in the “Extended PHP Information”. The config.inc.php configuration is the application configuration, and “Extended PHP Information” is phpinfo(), the PHP configuration.
What exactly is your “alllowed_html” line, and what version of OJS are you using?