Wordpress - Capabilities and Custom Post Types

After a quick chat with Magicroundabout who pointed out a useful resource from Justin Tadlock, it turns out that capabilities for custom post types don't actually exist unless you use add_cap to the role, for example for the following custom post type:

add_action( 'init', 'register_cpt_gallery' );

function register_cpt_gallery() {
$labels = array( 
    'name' => __( 'Galleries', 'gallery' ),
    'singular_name' => __( 'Gallery', 'gallery' ),
    'add_new' => __( 'Add New', 'gallery' ),
    'add_new_item' => __( 'Add New Gallery', 'gallery' ),
    'edit_item' => __( 'Edit Gallery', 'gallery' ),
    'new_item' => __( 'New Gallery', 'gallery' ),
    'view_item' => __( 'View Gallery', 'gallery' ),
    'search_items' => __( 'Search Galleries', 'gallery' ),
    'not_found' => __( 'No galleries found', 'gallery' ),
    'not_found_in_trash' => __( 'No galleries found in Trash', 'gallery' ),
    'parent_item_colon' => __( 'Parent Gallery:', 'gallery' ),
    'menu_name' => __( 'Galleries', 'gallery' ),
);

$args = array( 
    'labels' => $labels,
    'hierarchical' => true,
    'description' => 'Image galleries for teachers classes',
    'supports' => array( 'title', 'editor', 'author'),
    'public' => true,
    'show_ui' => true,
    'show_in_menu' => true,
    'menu_icon' => get_bloginfo('template_url') . '/images/imagegallery.png',
    'show_in_nav_menus' => true,
    'publicly_queryable' => true,
    'exclude_from_search' => false,
    'has_archive' => true,
    'query_var' => true,
    'can_export' => true,
    'rewrite' => true,
    'capabilities' => array(
        'edit_post' => 'edit_gallery',
        'edit_posts' => 'edit_galleries',
        'edit_others_posts' => 'edit_other_galleries',
        'publish_posts' => 'publish_galleries',
        'read_post' => 'read_gallery',
        'read_private_posts' => 'read_private_galleries',
        'delete_post' => 'delete_gallery'
    ),
    // as pointed out by iEmanuele, adding map_meta_cap will map the meta correctly 
    'map_meta_cap' => true
);

register_post_type( 'gallery', $args );
}

The additional capabilities should be added to a role for the permissions to actually work in the backend, including the 'administrator' - for example:

function add_theme_caps() {
    // gets the administrator role
    $admins = get_role( 'administrator' );

    $admins->add_cap( 'edit_gallery' ); 
    $admins->add_cap( 'edit_galleries' ); 
    $admins->add_cap( 'edit_other_galleries' ); 
    $admins->add_cap( 'publish_galleries' ); 
    $admins->add_cap( 'read_gallery' ); 
    $admins->add_cap( 'read_private_galleries' ); 
    $admins->add_cap( 'delete_gallery' ); 
}
add_action( 'admin_init', 'add_theme_caps');

I hope this is useful to others.

Additionally, the _x() translation function expects the second argument to be string $context, which is a short description, and the third to be string $domain. When not providing a description, use the __() translation function instead which has the string $domain as the second argument.

Add:

map_meta_cap => true

to your $args array. Look here, for more. Hope it helps!