Ctools overrides the local tabs behaviour and when you want to override the themable function you need to call ctools code as well.
<?php
function mytheme_menu_local_tasks() {
$output = '';
$primary = menu_primary_local_tasks();
$secondary = menu_secondary_local_tasks();
if (
module_exists('ctools')) {
module_load_include('inc', 'ctools', 'includes/menu');
$primary = ctools_menu_primary_local_tasks();
$secondary = ctools_menu_secondary_local_tasks();
}
if (!empty(
$primary)) {
$output .= "<ul class="tabs primary">\n" . $primary . "</ul>\n";
}
if (!empty($secondary)) {
$output .= "<ul class="tabs secondary">\n" . $secondary . "</ul>\n";
}
return
$output;
}
?>