Drop down menu does not work

Hi, thanks for this beautiful theme. Especially I appreciate a centred navigation that enables drop down menu and is responsive! Just what I was looking for!

But the drop down is not working.

In the Dashboard > Appearances > Menus I set secondary items (sub-items) by dragging them one stage to the right.

But when I click save menu they jump back to the right and become primary menu items.

Am I doing something wrong or the theme actually does not support a drop down menu – however in the demo site it does.