I’ve not found a way of doing this with the built in menu system either. I’ve loaded a menu plugin – just – and will look if that helps later.
For now though, I have made each menu page have content or links that mimic the items in the page/linked drop down menus. It’s not brilliant as a solution I admit, though at least as the drop-down menu disappears – or worse links to the actual empty menu page – at least the viewer still gets to choose a hyperlink to get to where they were seeking to go.
If ‘WP’ could possibly have the main menu page as a header, or something similar, rather a full blown page-link, if that were possible, it could be helpful: I think….
Of course more knowledgeable people than I may have other more practical solutions.
Cheers
Ian.