I have this problem, too. The shadowed rectangles and also this pattern. Like others said: it don't happen often. I can live with that. I really like this little camera. But I want to make sure, it won't get worse.
I had contacted Panasonic. All they said, it might be my sdhc cards fault, they have never seen something like that. I should try another card (had a class 10 card).
I think, if everybody contacts Panasonic, they'll have to take care of it.