The issue is that when you are hovering over a menu item, and you are aiming to hit a submenu item that is not directly to the right of the menu item. For example, if you are hovering over a menu item and wish to select a a submenu item that is to the right and down the screen, you will take a down-right path UX wise. Normally this would trigger the menu items below (before you make it to the submenu) and thus change the submenu items.