Building a Standards Converter

[`FRANK.C]

I have a DVD of This advert and was using it on repeat to view how well the interpolater was doing.  As the TV's moved around the screen it was easy to see the ripples created by poor interpolation, move along the horizontal(ish) edges of the TV's.  As the interpolater got better the ripples got less and less, but then I noticed that the ripples wasn't leaving some TV's. I couldn't understand why this was happening, that was until I watched it on 625.
The third TV in is particularly bad.  The DVD is of better quality but the ripples are as prominent.

Frank