When you switch from lanscape to portrait you can notice that the menu is reduced thus we can see everything in one page. However I think it would be better to follow what's mot apps does which it to have a consistency in the menu width. It is ok if we don't see the third panel, people need to use the menu option to retract the menu and see the third panel. This would make the menu looks good in anytime and not have a shrinking version in portrait mode.