I’m so sorry! I wasn’t originally testing it on anything, because I don’t own a smartphone. I was simply observing the behavior at small widths and in the Screenfly simulator, and I assumed that if hover worked, tap would not (because I thought it would act like a mouse click, which would open the parent item instead of the sub menu). But my husband does have a smartphone, so after your last post I asked to borrow it and tried it. Amazingly, it does work as you say! Apparently tap on a smartphone (at least on a brand new Galaxy S5) is a distinct event from a click – that’s great.
But one new problem occurs on the real hardware that was okay in the simulator – on the Galaxy S5 (default browser), the little arrow that indicates that a menu item has a submenu is not visible for some reason. There is no visible scrollbar, so that isn’t the cause. Here are screenshots with and without the submenu open.