Changing the display order of the menu can be a bit tricky. This is one of the few things that is actually why this is the BETA version of PageBuildr. The display of the order of the buttons on all menus and submenus can be adjusted by selecting a number from the list as shown below.
To ensure that you get your proper display order, first select the page you want to display last and select that number. Then, you have to go to each page within that menu and select the number of the display order in those pages and save changes. If you do it in this order, it should then be displaying the order of the buttons within a menu (or submenu) the way you want it.