Not sure whether to report this bug or not, since it is pure a user interaction thing.
For N-Theme: The selected item is grayed out as if was disabled while the other, which you cant press, are white.
Comment:
The checkout process is visible as menu items on the top in the order summary (the shopping cart that comes into view every time you add an item into the cart) but you cant press them. (why is the menu there at all? except the reason that it is reused from the real checkout process).