Worked it out. X-Cart/Javascript doesn't seem to like the two forms having the same name. I've made a second (copied) authbox.tpl and changed the "name" of the form from:
Code:
<FORM action="{$xcart_web_dir}/include/login.php" method="post" name="loginform">
to:
Code:
<FORM action="{$xcart_web_dir}/include/login.php" method="post" name="loginform2">
then I updated the a href tag of the button to reference this form:
I now have the original authbox.tpl on the side menu and the doctored authbox.tpl (authbox_mod.tpl) within the page. It now logs off regardless of what's pressed!
Dan