Suddenly I realised that I looked at the wrong track.
I played the tracks in the live video with sound part, where Graham is visible.
The Graham + Teddy tracks are recorded from Grahams NBTV vidicon camera, i.e. a Plumbicon camera tube, scanning directly on 32 lines 12,5 fps. It might have suffered from a problem called "beam bending". The files came to me via Grant Dixon. When I am back home I will have a close look at the file.