I have always vidded with .vob in Vegas, ever since it was Screenblast Movie Studio back in the early 2000's. I'm in a PAL region and I do remember having some issues with NTSC source but it was so long ago that I am not sure what they were or how I fixed them. However, this might help - have you tried the "match settings to source" button in your project settings? If not, go to the Project menu, then Properties, and on the Video tab at the top right there's an icon that looks like a bit of film. Click that and it'll take you to your media bin - just click on one of the .vob files that you want to match. Doing that should make all your settings the same as the source, which should, theoretically, remove any conflicts.