mac g5 has 2 HDs with diff osx (10,4/10,5) and one with 10,5 doesnt make programs work

thanks in advance for any help. i have a power mac g5 dual 2 ghz. it has two hard disks: one mounts osx 10,4, the other 10,5. when the g5 runs from the 10,4 disk all ok, when it runs from the 10,5 the programs that require 10,5 won't work (and won't install either). any idea why this happens and how can i fix it? thank you very much in advance.