Files and titlesets aren't the same thing.
The DVD-Video specs support up to a maximum of 99 titlesets on any DVD including single layer.
If I read you correctly then I think you're previewing the titlesets individually as opposed to playing the entire DVD.
DVDFab doesn't alter any of this by default so if the original has multiple titlesets then so will the backup.
That's not to say you can't change this but you'd need to have a specific reason for wanting to do so.
For example when users want to combine multi-disc or flipper movies.
So unless you have a need for this, just go with way it is on the original disc and it will play exactly the same way in your DVD player, software or otherwise.