Why is Grace Jones dubbed?

I bought this movie primarily because I am a Grace Jones fan. An Italian friend many years ago made me a copy of the song she sings in it "I'll Find My Way To You" which was taken from the movie's soundtrack I think. Grace later included a studio version of the song on one of her disco albums. However, in the movie the version is different and it is positively no her voice, it's dubbed. It's the smae in botht the Italian and English version on the disc. Very starnage as they make a selling pooint of it on the back cover, credits, and the composer Stelvio Cipriani talks about Grace in the intro and the bonus interview. The credits also mention another song by her "I Still Get The Blues" which doesn't seem to be in the movie. Can anybody solve the mystery?