Invalid setting for 'cache_wsdl'?

In netforum_admin_settings_validate(), there is this line:

'cache_wsdl' => TRUE,

However, according to this page:

http://www.php.net/manual/en/soapclient.soapclient.php

That option should be one of: WSDL_CACHE_NONE, WSDL_CACHE_DISK, WSDL_CACHE_MEMORY or WSDL_CACHE_BOTH