When the height of the menuItems are bigger than the frame size ,then the first & last menuitem will have the up arrow on the first visible menuitem & down arrow on the last visible menuitem . This arrow marks is an indication to the client saying that there is menuitems, but this is not happening on vista, so the client may think that there is a menuitem without title.

Note: you can verify the same with winxp.

Step to reproduce:
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1) Run the attached program.
2) Click on the Menu 'Menu1'.
3) Select menu 'SubMenu1:5'.
4) Select menu 'SecondLevelSubmenu1:5:12'. You can see some menuitem. Observe that the first & last visible menu item are not having arrow marks. This makes the client to think that menuitem are not having the title. If you see the same then the bug is reproduce.
5) Move the mouse of the first visible menuitem (which is not having the title). When the mouse is over the menuitem ,you will see the upper arrow . Next move the mouse the mouse on the last visible menuitem , Now you will see the down arrow on the menuitem.
6) Try to the do the same with thing with keyboard step (4). you can see only the upper arrow ,not the down arrow. so this is a bug.

I have attached the screen shot of the same.
I tested this on Vista beta2 (build 5342) on Mustang b81.