The reason things are scattered into multiple M2TS files is because some BD movies make extensive use of seamless branching features.
“Up!” is a good example of this.
If the viewer sets a different “Language” during setup, then entire scenes of the movie are replaced on-the-fly.
DVDs have done that too, through the use of “Angles”, and the WDTVs also don’t handle them properly.
Things like “Star Wars” have the opening crawl once in English, once in French, and once in Spanish, or several Disney movies have on-screen English and on-screen French (such as boxes/crates, newspapers (as Tony pointed out in “Up”), etc…), or some Disney discs have “pencil test” extras as a second “angle”.
When you play it on a stand-alone DVD player, it plays fine… just plays the selected angle and ignores the others.
But, when you try it on the WD devices, it plays each angle in succession… you get the Star Wars crawl in English, then again in French, then again in Spanish, or you get the Disney scene with the props and set dressing in English, then again in French, or you watch the theatrical scene, and then watch it repeated as a pencil test.
Any DVD authored with angles, unless you want the frustration of repeated bits, must have the angle you want ripped out, and then that file viewed, for the movie to play properly.
The BluRay discs are just doing the same thing under a different name. Instead of different “angles” to the stream, there are different “playlists”. Either way, as Tony says, if you have one like that, you need to “fix” it yourself when you rip it.