I'm not entirely clear what SCART does and doesn't have in it, but I believe it's still an interlaced signal. So, that means you're not having weird deinterlacing problems like I experienced. What you're seeing is, most likely, the result of bit-rot on the input to the MPEG decoder. High frequency stuff is where most of the bits go, so if you see errors there, that's exactly where bit rot would strike. You tend to see this effect on digital satellite more than on DVDs.

Possible failure modes that could be causing this:

- scratched DVDs
- bad focus / alignment of the DVD's laser pickup

To verify this, find somebody else's DVD player, replace your own, and see if the problem goes away.