Ok, I did manage to find some info about this problem here:

and here:

http://www.hometheaterhifi.com/the-dvd-benchmark/179-the-chroma-upsampling-error-and-the-420-interlaced-chroma-problem.html

It seems like it can be fixed or maybe reduced but this is a little over my head actually, maybe you could try to fix it, I don't know if it's really worth it. I have compared these two versions again and I now actually thinks Reivax looks almost better when you fiddle a little with the contrast/sharpness but I can also understand if you're not going to bother with it.