2.7: Migrating Plugin Admin Menus

Okay… What changed in WordPress 2.7 in relation to add_submenu_page()?

I develop the WP125 plugin, which creates a top-level “Ads” menu with three submenus. It worked perfectly in 2.6, 2.5, and 2.4, but in the 2.7 trunk the submenus don’t link properly (oddly the top-level one does fine).

For example, the Add/Edit page is supposed to be this: /wp-admin/admin.php?page=wp125_addedit but in 2.7 trunk the link target is /wp-admin/wp125/wp125.php?page=wp125_addedit.

The relevant portion of the plugin source is:

add_menu_page("125x125 Ads", "Ads", MANAGEMENT_PERMISSION, __FILE__, "wp125_write_managemenu");
add_submenu_page(__FILE__, "Manage 125x125 Ads", "Manage", MANAGEMENT_PERMISSION, __FILE__, "wp125_write_managemenu");
add_submenu_page(__FILE__, "Add/Edit 125x125 Ads", "Add/Edit", MANAGEMENT_PERMISSION, 'wp125_addedit', "wp125_write_addeditmenu");
add_submenu_page(__FILE__, "125x125 Ad Settings", "Settings", MANAGEMENT_PERMISSION, 'wp125_settings', "wp125_write_settingsmenu");

What’s going on here? How should I fix this? It needs to work in the upcoming WP 2.7, as well as in previous releases.