I found a second example of my issue (submenus not appearing in Mint Menu, although they're in the Gnome Main Menu)...
I just installed gnome-games using Synaptic. The install put some games under the top-level "Games" category, but others under a "Logic" subcategory.
In the Mint menu,the "logic" subcategory doesn't show up at all. The games in the top-level "games" category appear, but the "logic" subcategory and the games in it do not appear. I can see the subcategory and the games under it in the gnome main menu (as well as in the gome main menu prefernces preferences, where the category is tick-marked to be displayed), but not in the Mint menu.
Although the problem may be peculiar to me (but I had done a clean install of Mint 8 and have done no configuration changes), I begin to suspect a Mint Menu problem with subcategories / submenus.
Is anyone else seeing the same thing?
Regards, Rob L