WordPress Custom Menus Issue

In my template I’m using calls like this to output some custom menus:

<?php wp_nav_menu(array('container_class' => 'secondary-navigation', 'theme_location' => 'secondary')); ?>

Ever since upgrading to WordPress 3.1.4 I get the full list of pages output on instead of the custom menu

I’ve seen fixes (via google) saying I should add the following to fix this:

'fallback_cb' => false,

While I understand why this might fix things for some people, when I do the menu doesn’t output at all (not just unstyled content, no html is echoed).

My theme is heavily based on the twentyten default theme (from a code point of view), so I guess my question is does anyone have a fix which doesn’t involve setting the fallback callback to false…

And/or does anyone know if this issue also exists in the latest RC for the new version?