Pay attention that WordPress has 2 built-in post types: ‘post’ with capability type ‘post’ and ‘page’ with capability type ‘page’. When you set capability type of your custom post type as ‘page’ you will not see any new capability at ‘Custom capability’ as there is a set of WordPress built-in capabilities, like ‘edit_pages’, ‘delete_pages’, ‘publish_pages’, etc.
