probably a stupid question, but why not use DVDDecrypter or SmartRipper to rip the VOB files? using one of those programs may or may not help sort out this problem, but they're freeware so it's worth a shot.

also, even a better idea - why not just jot down the timecodes for the chapters of each video, then rip the M2V (video) and AC3/PCM/MPA (audio) streams as their own demuxed file; then, simply import the audi and video streams and insert the chapter points. i know it might be a little more work, but it should work fine.

other than that, i don't have many clues. to me, it seems sort of iffy to import VOB files directly into an authoring program... mainly because that is a "newer" feature for authoring programs. importing straight-up audio and video streams is a much more "orthadox" method that would seem less problematic.