I'm actually quite sure that it is an issue of synchronizing the double-buffering to screen refresh -- or something that appears the same -- and there really is no excuse whatsoever for not getting it right. It's actually interesting how difficult it is to convey what is happening, short of showing people. I can't take a screen shot with it, I can't really take a video of it... I can only try to describe it. Apparently our communication is still somewhat limited, despite all our technology.)
I haven't seen much deinterlacing issues with iTunes -- which is good, because I have seen other videos where it IS and issue, and it's really aggravating!