GTK L&F: swing GUI menu shortcut does not work properly

This bug is tracking the issue that JMenu mnemonic activation with the GTK L&F is inconsistent with native. The original description for this bug is below but, as it was slightly in-accurate, I'm updating it here.

With SwingSet2, under the GTK L&F do the following:
- Hit ALT + T to bring up the "Themes" menu
- Hit ALT + F
The "Fonts" menu item of the "Themes" menu will be selected. This is incorrect - ALT + F should do nothing. Native behavior seems to be the following:

Hitting ALT + [Menu Mnemonic] should bring up the menu.
After this, ALT + [key] should do nothing.

However, there appears to be one subtlety. If a menu is showing but no child items are highlighted, then ALT + [key] can do something. To see this, open a top level menu with the mouse (not selecting any children) and then try using ALT + [key].

I cannot describe all of the behavior here, but we need to investigate and make our menu activation behavior match native.
###@###.### 2004-06-07


Original Description:
---------------------
This is related with 4983388 and it has been almost fixed, mainly in
the shortcut activation. However, the activation behavior between
the menus is strange.

For example, there are 4 menus in SwingSet2 demo: "File", "Look & Feel",
"Themes", "Tool Tips". To press Alt + T for showing up menu items of
"Themes", then press Alt + F to move the menu to "File" but "Fonts"
menu item of "Themes" menu will be unexpectedly chosen.

If "Fonts" menu item is expected, only F key is pressed without Alt.