The above images are both renders; the Sony CoDec and the system default Codec (which I assume is Microsoft). The source material was identical in both renders. The non-Sony render looks just like the source DV footage.
I created the colour chart artificially because it showed off the problem very clearly, but I have been doing a (pardon my French) shit load of tests with real camera footage with the same results (even with the uncompressed option). It's harder to see with "normal" footage. I started to see the problem with greenscreen footage. The transition from green screen to subject matter became very blocky.
But just so you know: I made the colour chart in Combustion. It of course is beautiful 24bit RGB, with sharp edges. I rendered the chart to DV, where it did pick up some DV artifacts, but no more than expected. I used this DV source for the above test, but as I say, any DV footage can be used, this one just shows off the problem very clearly. The way in which this source footage was generated is not part of the problem.
I tried all sorts of iterations, but every time I rendered to any CoDec other than DV, the Sony CoDec would butcher the chroma. I even tried forcing Vegas to interpret the source material as progressive and rendered both interlaced and progressive. I also forced the image to go through a complete recompression by adding a slight colour correct or putting some text on it. The Sony CoDec always looked fine when rendering to DV, but otherwise it was crap.

I would really like to use the Sony CoDec because it appears to be the only DV CoDec that doesn't clip off highlight detail (anything above 235cv/100 IRE) when it does its YUV to RGB conversion.
FYI: I'm always exporting footage from my Vegas edit to do VFX work in Combustion. I render out select shots as DV, and Vegas just make a perfect copy of the footage without recompressing (as it should). Even the highlight detail is still there. Problem is, when the footage come into Combustion, the highlight detail is clipped off in a standard YUV to RGB conversion.
I discovered that if I use the Sony DV CoDec and export to Huff (or Alpary or Uncompressed, etc.) the highlight detail remains, and since it's now RGB no conversion is done when it's pulled into Combustion and all the highlight details are there.
That's great! I love it! But then I noticed what it does to the chroma. Retch!
I would much rather lose a bit of highlight detail than butcher the chroma so much.



Anyway... In a nut shell...
Sony DV CoDec works fine so long as the final render is back to DV. ANY other kind of render format has crappy chroma atifacts.
The solution is to only render to DV or use a third pary DV CoDec when rendering to a non-DV format.
Only problem is, every other DV CoDec I've tried chops off the hightlight detail.

Why can't I have the best of both worlds?