Access Denied on nodeapi load case

Whenever I update a node using a node form (even as admin user), the redirected page will always result in the 'Access Denied' page.

I've isolated this to the use of the 'drupal_get_breadcrumb' function when using nodeapi on load. The error doesn't appear if I comment out the function call:

function gem_theme_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
  switch ($op) {
    case 'load':
      $breadcrumbs = drupal_get_breadcrumb();
    break;
}

Any ideas? The breadcrumbs are a huge feature of my module.