Yeah it IS odd, launchbox should default to the first disc, unless you specifically change it manually which you say you haven't so i am at a bit of a loss to be honest. I don't recall hearing of this happening before, but i could be wrong. One thing i would check is that each disc is named exactly the same except for the disc number, it may be disc 4 has a capital letter the others don't or something like that, making it appear at the top of the list as it's a different name??