Sony G900AP - troubles with superimpose feature

Hi!

Some days ago i got a very nice Sony G900AP, 1MB Ram and so on.
When testing the superimpose-feature (i.e. mixing video input and computer graphics), i could observe one strange thing:

The picture of the video input (both, REF IN and SCART) comes clear and bright.
The text-characters generated by the videochip and displayed on top of the video-input are clear too, but each pixel has got additionally a black shadow showing to the right side of the screen with a length of about 1cm.

Has anybody ever observed such an effect on a Sony G900AP?
What could be the reason and is there a possibility to repair it?

Btw, i never had such a problem on the NMS 8280...