@madshi
I compared the chroma upsampling a bit and I noticed that madVR's frequency response is noticeably lower than ffdshow's (HQ upscaling and Lanczos resize to 1920x1080). In both cases I used Lanczos4 for resizing.
If you look at the middle of the Siemens star you'll see that the lines are not fully resolved. Without the resampling option in madVR the resolution stays almost the same, but aliasing occurs.
ffdshow:
madVR with resampling:
madVR without resampling:
The problem is even more visible at the burst pattern. The amplitude of the chroma signal begins to fall at 1MHz.
ffdshow:
madVR with resampling:
Is this a bug or just a side effect of your upsampling algorithm?