The first movie that was released in both East and West Germany at the same day (10 March 1988).
When Paul comes home for the first time, he accidentally tries to open his neighbour's door instead of his own. He walks down the stairs afterwards and opens his own door. These two doors are actually the same. The pattern on the lower marble wall is exactly the same, the name on the mail box is the same (also too short for his last name "Winkelmann"). Furthermore, the shadows on the wall and the door indicate that the shots were taken on different times of the day.