West German gliders ending up in East Germany used to be a regular thing (like one every two or three years until 1989).
There was an ADIZ along the border on the West German side (about 30 km deep), and ingress without flight plan into the ADIZ was treated as a felony, but gliders used to be tolerated by allied forces to fly within the ADIZ (sometimes for stretches of 200 or 300 km).