How to display children for a MenuItem with a Command?

I’m trying to avoid pre-populating menus due to performance reasons, so I want to populate the sub-menus only when the top level menu item is clicked.

If the top level MenuItem has a Command to process the incoming click, it CAN have visible children and with the debugger I can even see the server sending them to the browser…

…but the browser won’t actually display them…

…until I set the top level command to NULL.

So far the best result I’ve managed is to populate the sub-menu on the first click, set to the command to null and then on the SECOND click the sub-items are actually shown.

Is there a better way to do this?