I checked the Show as Expanded in my Menu item but I can't see the dropdown menu I created.

I'm experiencing this same issue. I only see that the menu item has a drop-down on that specific main nav landing page.

I'm currently researching this issue. It's super annoying. I'll post up my solution, if I find one.

I managed to solve this by analysing the difference in js files between the 7.x-1.3 and the 7.x-2.x-dev.

I added these lines to js/custom.js

	jQuery('#main-menu > ul').superfish({ 
		delay:       500,								// 0.1 second delay on mouseout 
		animation:   { opacity:'show',height:'show'},	// fade-in and slide-down animation 
		dropShadows: true								// disable drop shadows 
	});	  

	jQuery('#main-menu > ul').mobileMenu({
		prependTo:'.mobilenavi'
	})

I then copied superfish.js to my themes js folder and added this line to nexus.info

scripts[] = js/superfish.js

You only need this line if you want the >> symbols that signify the menu item is droppable. Otherwise it's not needed.

You are now able to theme the dropdown menu as you please.

Hope this helps someone or at least points them in the right direction.

Cheers,