Dropdown menu moving to the left when you hover over half way the page

When you are at the middle of the page (scroll to middle of page), and you want to select another menu item from the dropdown menu it is not at the same position as when you hover over the menu item when you are at the top of the page.

How to fix this?

Menu items should always be a little indent to the right, at the same position as when you are at the top of the page.

The page I need help with: [log in to see the link]