Hidden Accounts unhiding?

I'm a bit confused. I made an image with our Casper management account and our corporate local admin account, both hidden... I verified this by installing on 3 different Macbook pro laptops (2008, 2009, 2010).... However when I image a MacPro (desktop) the accounts are no longer hidden. I first noticed this when I had Casper making it's own account when a machine was imaged. It would remain hidden until I installed Adobe CS3... then all of a sudden the Casper account would unhide itself. It seemed to be the only app that would cause it to unhide. So this weekend I made a new InstaDMG image with both the Casper and our Local admin figuring that would take care of the issue.