Without knowing the in's n out's i can't say for sure, but it sounds like there is some kind of copy protection on the disks - making them bigger when you try to copy. Football Manager uses this method - about 650mb on the disc but when you copy there isn't enough space.
I'm neither sure how this works or how to get around it! Sorry.
But hopefully i'm wrong and some other helpful chap or chapess can shed some light.