Sub-Menu items not appearing

[ThyPirateDave]

When sub-menu items are moved or created, on occasion they do not function properly. All the right conditions are set, such as in the example, but the sub-menu will not fire. I find this only affects 3rd links, that being the top first menu and sub-menus of that are not affected but "sub-sub-menus" are.

Replication: 20%~ but when you find one that doesn't work, it tends to replicate at about 95%
Affects all pages
Tested in Firefox

I have tried correcting it by removing the sub-sub-menu item and re-adding it. I've tried re-adding it under a different name. I have tried a variety of things to get it to display. It may work for a moment but then the item disappears again after any other unrelated change to the menu.