register_post_type exclude_from_search argument not working

I have a post type registered with this code, however 'exclude_from_search' => true seems to have no effect as I still find output in the search page. Am I making some mistake?

add_action('init', 'abundant_life_slides_register');
function abundant_life_slides_register() {
    $args = array(
        'label' => 'Slides',
        'description' => '',
        'public' => true,
        'show_ui' => true,
        'show_in_menu' => true,
        'show_in_nav_menus' => true,
        'has_archive' => false,
        'capability_type' => 'post',
        'hierarchical' => false,
        'rewrite' => array('slug' => 'slides'),
        'query_var' => true,
        'supports' => array('title', 'editor', 'thumbnail', 'page-attributes'),
        'labels' => array (
        'name' => 'Slides',
        'singular_name' => 'Slide',
        'menu_name' => 'Slides',
        'add_new' => 'Add Slide',
        'add_new_item' => 'Add New Slide',
        'edit' => 'Edit',
        'edit_item' => 'Edit Slide',
        'new_item' => 'New Slide',
        'view' => 'View Slide',
        'view_item' => 'View Slide',
        'search_items' => 'Search Slides',
        'not_found' => 'No Slides Found',
        'not_found_in_trash' => 'No Slides Found in Trash',
        'parent' => 'Parent Slide',
        'exclude_from_search' => true,
));

register_post_type('slides', $args);
}