Just noticed that when selecting a sub-menu item from main navigation and you are directed to that page, the current page you are on is no longer visible in the main menu navigation. Don't know if this is by design or not and I can't find anything that would prevent this from happening and the users are not wanting this menu item to disappear, so thought I would put the question out here to determine if it is something that is configurable or not.
When you navigate to a page that is a sub-menu item in the menu control, that page could disappear from the menu if the menu is configured that way. There are different types of menus that you can create as documented in the help.
By default, when you create a menu, it’s generated from the pages and site map links in the Site Map folder in the Site Pages view. However, you can also create a menu that’s generated from the pages in the Landing Pages folder or from the child or sibling pages of a site page.
So, if the menu source is set to Child Pages, the menu only shows pages that are children of the current page. When you navigate to a page it will no longer show up in the menu. Also, if the menu source is set to Landing Pages, the menu only shows pages in the Landing Pages folder, so if the current page is not in the Landing Pages folder it would not show up.