Missing arrow under selected menu item

Newest results:

I double checked the menu item configuration. Found that some are different configured. So I set all menu items to the default configuration. Global config.

Than tried it again with the new folder mod_menu from the 2.5 version. NO changes.

Than changed the default.php to the original version. NO changes.

Than tried it without the folder mod_menu. NO changes.

Everytime the arrow below the menu is doing whatever he wants, but not what he shall do.

Any further ideas?

This can cause that, i see you have multiple menus, make sure if each menu item is only created once as instance , and menu items pointing to same thing in other menus are only aliases for that menu item .