My users are confused -- and I note this is the designed behavior on the demo theme as well -- 

make the browser mobile width to get the menu to collapse.

Then try clicking on one of the menu words -- it won't open the sub-menu items.

But if you click on the v icon - the menu does reveal the sub nav.

Most of my users see the word and click it -- they don't see the V  and generally are not curious people so they don't wonder what it's there for and wonder what will happen if they click it... instead they just complain that it's "broken"

As far as I can tell, this is all browsers:

http://cl.ly/image/3u1u3Z0R2D02

Bingo!

For future keyword searchers:

Make mobile menu activate when parent menu item is clicked on instead of just clicking on arrow

Mobile menu show child nav when clicking on parent nav item instead of arrow