There are at least two different issues being discussed here. I'd read about the issue Prez808 is describing elsewhere. My understanding is that that can be fixed by disabling Contrast Enhancement or some sort of auto luma setting. That's not what I'm running into. Here's a screen capture of the issue I'm seeing (along with the corrupt frames reported in the debug menu):
I get that black corruption appear from the bottom every second or two, along with other MPEG-2 pixelation artifacts and audio stuttering. Like I've said before, this only happens on certain channels. To be sure, when plugging in the same tuner and testing the same channels on a different computer, I don't have this problem. I just tested this same channel when the tuner is plugged into my laptop, and it displays without any issue.