¿¿¿MenuItemHeight???
Código:
Extraído de la ayuda de Delphi 7
Occurs when an application needs to determine the height of a menu item.
...
Write a MenuItemHeight event handler to calculate and return the height needed for menu items when the TStyle object customizes their appearance.
Supongo que debes cambiar eso por
Items.Count -1.
Saludos!