add_menu_page and Dashboard menu item

[arena]

I have a plugin : MailPress that i am currently adapting to 2.7.

In the plugin settings, i have the option to make all mailpress menu in one place (with add_menu_page)

When this option is activated,

• When i am on the WordPress Dashboard pane,
  • the urls of the menu items of my plugin are this type : ​http://127.0.0.1/wp27/wp-admin/mailpress/mp-admin/mail-new.php?page=mailpress/mp-admin/mails.php which leads to a 404 ...
• When i am on any other menu options,
  • the urls of the menu items of my plugin are this type : ​http://127.0.0.1/wp27/wp-admin/admin.php?page=mailpress/mp-admin/mail-new.php and that is GOOD !

Btw, the bug disappears if there is more than one menu item in the Dashboard menu

i attach the 2.7 release of my plugin.

[DD32]

see #7841