I have an Octavia from 2015 with parking sensor in the back.

 

When I shift the transmission to "R" the screen with the parking sensor screen comes up which is fine. When I am done driving backwards and put the lever in "D" the screen changes to my radio and I begin to drive. Then for a few (about 2) seconds the parking sensor screen comes on again on before it changes back to radio for good.

 

Is that normal behaviour that the parking sensor screen appears for a while when I begin to drive forward?

That's normal. It turns off at 15mph iirc.

Are you still rolling backwards when you select D or are you completely stationary?

My parking sensors give a loud beep when I select 1st gear after reversing when the car is still moving backwards.

Its kind of a warning that you moving in the opposite direction to the selected gear.

 

Maybe the screen works the same with the DSG?

No I am never rolling backwards when changing to "D". 

My 2016 still shows the sensor map for a few seconds after selecting Drive and moving off. I don't remember seeing it ever flick off and on though. Probs due to me going straight from R to D in one move and looking where I am going.

Mine doesnt do this but my sons VW Polo does!