So I would say no to that. Clear you cache files on the server and on your computer and double check your server and see how they are running sessions. Do a phpinfo() You might find it's the way your server is configured and not XOOPS at all. That is what I would do if I were you.
<?php
// Show all information, defaults to INFO_ALL
phpinfo();
// Show just the module information.
// phpinfo(8) yields identical results.
phpinfo(INFO_MODULES);
?>