maybe your PS3 is trying to do you a favor
seriously though, jumpy playback sounds like it might be a faulty disc. i did a quick google search and couldn't come up with anything commonly reported. any friends who have a bluray player you could test the disc out on? or is it too much of a hassle to return the disc for a replacement? if you can't do the former, the latter seems like best solution. i haven't come across any disc that hasn't worked on my ps3, so i'm guessing it's the movie itself, not the system.