As I posted above I saw problems starting somewhere in chapter 18 until somewhere in chapter 23. When I have some time later this week, I'll try to be more exact.
Playing devil's advocate (since I may be a bit underwhelmed by Episodes I and II, but still enjoy them overall) there is a well-known phrase in theater, "If it ain't on the page, it ain't on the stage."
I double checked and the video problems, in the form of severe combing, appear to start at exactly the start of chapter 18, and end at the very beginning of chapter 22. The combing problems disappear if I switch my player to interlace mode.
I am not familiar enough with the film to know if these chapters comprise the additional scenes not originally released in the US theatrical version?
How exactly does one look for incorrect progressive flags, and what softwear would be needed?
Is the problem simply that the disc was encoded with a flagging error that will cause problems with certain DVD players, or is it that the transfer was not made properly from the source (i.e. it was not really mastered in high definition even though the box says so)? Is there a way to tell? I'm willing to take the risk with my player, but I want to know if the transfer was acutally botched no matter what.
This kinda gets technical, compression-wise, but if the encoding for the film was done in sections - or if a certain section came from another source (i.e. deleted scenes from a PAL or video master; I'm not saying it was done here, I have no idea) - then it is possible for a particular area to be improperly flagged.