I added a custom top level menu with add_menu_page and it works great. I then added a custom post type and used 'show_in_menu' to add the custom post type to that custom menu and now that is taking over the default admin screen for my top level menu. Is there any around this behavior in WordPress? Before the CPT admin.php?page=custompage was the default for my custom menu but now it is edit.php?post_type=book which I only want as a submenu item.
I have minimal code to recreate the problem using code from the codex at http://tegenkamp.com/wp-content/plugins/cptdev/cptdev.php.txt to help anyone wishing to recreate the issue on a development installation.