Some systems seem to manage the bandwidth and disc access by giving you a copy of someone else's stream if they are already watching the movie you select. Many users will just watch the movie from part way through instead of rewinding it to the beginning (which will force the streams to split), so they can cheap out on the resources a bit. Basically they are taking advantage of their users' fear of technology and the fact that at least half the airplane has enough trouble selecting a movie, and isn't going to try anything fancier. On systems like this (which are usually retrofit on older infrastructure), I have seen stuttering after splitting my stream off by rewinding to the beginning, occasionally to the point of being unwatchable. But on newer systems, there seems to be sufficient bandwidth to stream without stuttering.