hook_uc_checkout_complete problem

I'm having an issue with this hook.

I have the following code in a module:

function my_module_uc_checkout_complete($order, $account) {
drupal_set_message('TEST');
kpr($order);
}

When I complete checkout I get the test message but the contents of the $order object (Devel is installed) is not displayed.

Any idea why this doesn't work, or how I can access the contents of the $order object from this function?