I thought I would try something. It didn't help, but it might help shed some light on the problem.
I initially thought DVD2OneX was ignoring the last VOB file so I decided to compress the movie to 3824 Gig and then add the missing VTS_01_6.VOB file (which is 648 meg) later. But when I looked at the files this time, the VTS_01_5.VOB file was missing. Now I see what DVD2OneX is doing, it simply compresses video data to fewer VOB files.
Now I certainly know nothing about the inner workings of DVDs but it seems to me if an episode DVD is formatted to look for a certain VOB file instead of some kind of marker within one of the VOB files then the copy won't work if some VOB files are missing. This may be the reason why people are having problems with some episode DVDs. If this is the case, then DVD2One should retain the same number of VOB files during compression... at least for episodic DVDs.
My assumption is based solely on the fact that this DVD has 6 episodes which evidently correspond to the main 6 VOB files. I may be wrong about this but it will be interesting to find out whether or not I am.
I should also mention that when I view the VIDEO_TS folder for this DVD in DVD2One it not only lists each individual episode with title number and a time of 30 min. each, it also shows all episodes combined into one title with a time of 3 hours. This makes absolutely no sense to me.