There would be good to have a choice from all items in the Main menu like in this example:

  • First
  • Second
    • sub page 1
    • sub page 2
  • Third
    • sub page 1
    • sub page 2

So when I am on the main page, there are only links for the First, second and third page. When I choose Second, now suddenly a sub-menu appear for the items under it, but not for the others onder Third.

It may be only short change in the page.tpl.php file at lines 41-52.