2 versions?

Recently I watched a version of this movie which was complettely different from the version I remembered watching some time ago. They were both synchronised in english (why do they do it anyway? what in the world can't I hear an old Jackie Chan film actors in original language, not some stupid american voiced dumbasses? - but that's another topic), but the dubb actors were different, the dialogues were completelly different, to the point that 2 films got almost complettely different plots, and even the sound effects and music in both versions are different.
Why do they to that? And I got a feling that neither of those 2 versions is the originall one, which is a real shame, cause i happen to be a big Jackie Chans fan, even thougn his movies are silly and low budged, I think they are lots of fun.