Hmmm, ( scratch head, bite nails and plod around the room for a bit.... ) That should not happen really...unless....
On the origional DVD, does all the speech come from the right speaker? if so then it might be taking the left side audio from another language and the english soundtrack as a "Add on" on the right speaker.
I suppose the only way to find out is to re-master the DVD, leave one of the other languages on, and try again (use a virtual drive on your PC to save blank discs).
Otherwise I'm stuck.