Drop-Down Menus Don't Drop Down Fully

The drop-down menus in my membership site display fully the first time around, but when I try to go back in, they only display partially (e.g. I have 10 pages in the drop down menu, but only 5 appear.)

If I click the “Home” tab and then go back to the drop-down menus, they display fully completely.

Does anyone know why they only display partially?

Thanks,

Arny