.NET MenuItem.IsSubmenuOpen = true only works the first time

I have a ContextMenu with some sub-menus that have items (MenuItem) that can be selected. When the ContextMenu is opened, I want to recursively open the currently selected item. So, I have the following code:

    protected override void OnOpened( RoutedEventArgs e ) {
        base.OnOpened( e );
        OpenCurrentSubMenu( Items );
    }

    private static bool OpenCurrentSubMenu( ItemCollection itemCollection ) {
        foreach (MenuItem item in itemCollection) {
            if (item.IsChecked) {
                return true;
            }
            else if( OpenCurrentSubMenu( item.Items ) ) {
                item.IsSubmenuOpen = true;
                return true;
            }
        }
        return false;
    }

I also have some other code that ensures that only one item is checked.

This seems to work great the first time I select an item in a sub-menu. When I re-open the ContextMenu, the open sub-menus cascade open to the selected item:

However, when I leave the context menu, and re-open it a second time, the selected menu does NOT open:

Does anyone know why and how to fix it?