Think about it. The DIS/board computer and the Navigation unit are two separate components. The DIS only knows the board computer stuff. Once it receives over CAN the message from the Navi "Hey, here I am", it reorganizes the layout, moves the audio source and temp up to the first two lines and gives the Navi access to the middle part of the DIS.
Now it's the Navi which decides what to display there. If you are not in route guidance and have the compass checkd, the Navi displays in its assigned section of the DIS the compass, and because it knows, it displays the street youare on as well. If you are in route guidance it will only show routing information, part of which is the street name you are on or you are going to be on.
So, if you deselect the Navi screen to get back to your board computer, it will stay there until you activate route guidance and the Navi tells the DIS again "here I am". The Navi doesn't know about your fuel consumption or distance to empty. And the DIS/board computer doesn't know about the street you are on.
It's the same in my A4 B6. If I deselect the navi screen it stays in board computer mode until a) I turn on route guidance or b) I switch back to the navi screen. Even if the lady thinks she has to say something, the DIS will not switch back to the Navi if you manually moved away form the navi screen.