I recently bought the karaoke CD of HSM2 for a film project (I needed the instrumental track of Fabulous for a shopping montage as a temp track... don't ask), when I noticed that the Sing-Along tracks feature the original vocals at a lower volume than the soundtrack's mix.

If you own more than one of these CDs from the Disney Karaoke Series, is this common with the sing-along tracks? I'm just curious, because I never encounted this with any of the other Karaoke CDs I've used.