It's definitely a problem with the way the DVD was mastered, but what I'm saying is that the player doesn't handle the problem well. When I try those two DVDs on other DVD players, the combing problem doesn't occur. I honestly don't know much about flagging per se, but when I researched about combing problems, flagging was the only cause I can find.
It's an unusual problem. At a certain part of the movie, the combing problem would occur and remain that way. If you stop the disc and resume it, the problem goes away. It's as if something on that part of the disc is deactivating the DVD player's deinterlacer or something. Then I guess when you stop & play the DVD, it reactivates again. It's weird, but forgivable as it only happened on 2 DVDs.