Okay, that’s interesting. I’m starting to think that it’s a playback problem, specific to my system (and, by coincidence, maybe to the other user’s system that I previously tested on).
When I scrub frame to frame on my footage, I do get the funny lines appearing sometimes as the frames are resolving, but it isn’t on the still frames.
I’m on a Macbook Pro, 2.4GHz Core 2 Duo/2GB/ 256mb VRAM. Could it be that I need a stronger video card to playback footage of this size?