Main Menu problem

Hi,
Suddenly I encounter en problem with the main menu.
We have en quite extended menu with several subs and sub-sub.
At the moment it’s
8 main-levels, with 25 sub levels, 72 sub-sub and even 20 sub-sub-sub

The menu configuration in the drag and drop window does not show the entire tree. Up to a certain amount. The menu-bar shows the links from the footer area and the login/logout option is gone. The navigation setting in appearance is empty and when we set that to the menu we have configured and save it, the menu-bar is temporary okay up to the amount of levels as shown in the drag and drop window. When we select a menu item to add or we add the login/logout function and save it, the entire menu-bar is thrown over again.

Please help because this is pretty annoying and a big issue for us.

This is the site:
http://www.weertersportraad.nl

greetz, Michel