Menu is wacky on iPhone

On the iPhone 5s, WordPress 3.8 and Decode 2.9

When you have a header menu and tap on a top level item with children, when the sub-menu opens, the main menu wraps under itself. It’s hard to explain, but it’s like the horizontal menu changes itself into a vertical menu from the current item onward. It’s strange. The opening of a submenu causes the main horizontal menu to wrap.

So you have menu items horizontal, then the vertical sub-menu, then the horizontal items after the menu are now underneath it… not hidden, but after the flow. Nothing like the desktop version and nothing like I’d expect it should look.