I've encountered this problem with 2 discs now... During playback the picture will suddenly start to become interlaced, to the point where eventually the entire screen is a mesh of blurry lines. The problem is solved simply by pressing 'Stop' and then 'Play' again - bingo, the picture is progressive once more.
It has only ever happened twice during 2 different discs, and once the disc was stopped and re-started didn't happen again in playback. I've gone into the setup menu to make sure I've got everything switched to "progressive mode" - all OK there.
It's not a big issue but it's annoying and rather disconcerting with what is otherwise probably the best DVD player I've had in the 12+ years since first getting into DVD.