Responsive editing not saving in just mobile

Hello, I thought that i could edit the large screen layout in responsive mode as a mobile screen and save it. So that the layout on the mobile screen would be saved as custom layout and would not affect the large screen layout? But it is not happening. When I do a custom mobile layout it does the same changes to the large screen layout. What good is responsive mode if it will not be specific to mobile screen?

This doc seems to say that it can be done:

Can it be done? Thanks, Clay

Can someone Please answer this question? This is driving me insane!