Big site menus cannot be reordered

Big site menus cannot be reordered in the 'edit menu' dialog because the menu items cannot be dragged outside the visible part of the menu.

For example, the attached screenshot shows the 'documentationmenu' from onehippo.org, with about 280 items deeply nested. Reordering the top-level menu items in there is impossible.

Steps to reproduce:
1. create a site menu with 12 items or more
2. try to position the first item below the last item

Or:
1. create a site menu with 3 top-level items that each have about 8 sub-menu items
2. try to position the first item below the last item

Expected: I drag the first item down. When I reach the edge of the visible menu, the menu area scroll down automatically until I've reached the last menu item
Actual: I drag the first item down. When I reach the edge of the visible menu, nothing happens

Being able to expand/collapse menu items would help a little bit, but it still would not solve the problem entirely.