the dvd vendors in thailand might seem inexpensive at 100 baht (us$2.50) per disc but the vendors in china blow them away with pricing at 7rmb (about US$0.90) per disc. at that price one can't expect the discs to be perfect, and i find that around 25% of the discs either don't work at all or (worse) flake out towards the end of the movie.
the captions, especially for new movies, are done in china- often translated directly from the chinese that was translated by a chinese person watching the movie and trying to scribble down the script. just like the 'chinese whispers' game (i wonder how it got that name?) the results can often be quite different from the original dialogue.
in some cases the captions are completely off- either they started out ok and the captionist got bored and decided to write whatever he felt like, or they are from the wrong movie.
fahrenheit 9/11 was the first dvd i watched in china. the captions are obviously from another movie with a very very different subject matter...