Well I have the Blues Brothers movie and the original soundtrack, and the music in the movie is higher pitched than then soundtrack. It has occurred to me in more movies too.
Top 40 radio stations will sometimes raise the pitch of songs to make the station seem to be more upbeat and move faster. I assume it is done on movies for much the same reason… to fit better with the scene.
It might not necessarily be the pitch. I know from experience that sound designers have to compress music in various ways to get it to sync up correctly with the rest of the movie. It could easily arise out of something like that.
If there is dialogue overtop of the music, they may change the pitch to prevent the two different sound tracks from confusing the viewer. Usually, they can speed up or slow down a song without altering the pitch. In older movies, maybe this wasn’t possible, though…