When a sub-menu item is selected, the sub-menu accelerator key doesn't display the sub-menu

When a sub-menu item is selected, the sub-menu accelerator key doesn't display the sub-menu.

To reproduce:
1) Using the Menus from Qt Examples and Demos - Main Windows (examples/mainwindows/menus)
2) Hold the Alt key down
3) Press the 'e' key to show the Edit menu
4) Press the down arrow key to select the Format sub-menu item
5) Press the 'f' key - the Format sub-menu isn't displayed.

If you press the up arrow key to select the Paste menu item, then pressing the 'f' key will display the Format sub-menu.