Tearing on white images with Panasonic TH-42PWD4

[mtcs]

A few months I made some changes to my home theatre setup.

My TH-42PWD4 now uses a Joytech 245C switch box to send various component signals to the PWD4.

This includes a prog-scan Pioneer DV-575A and a Sky+ unti (Pace PVR3).

The Sky+ has a QED QVC Scart RGB to Component converter.

Here's the problem ---> playing back certain material through Sky+, anything with a solid white background, I see what I can only describe as a tearing pattern across the top of the screen. A good example of this is the 'Grays Anatomy' picture you see on Libing TV when the program breaks for advertising.

So far i've only seen it happen on solid whites.

Is this something to do with the RGB to Component conversion or the Joytech switch box?

Is there something that can be tuned in the PWD4 so it displays a solid image instead of tearing like it does?

In all other respects, the picture quality through Sky and DVD's is excellent.