After that installation reboot, the bootloader is supposed to attempt to boot from the CD but ask explicitly if you want to boot from the CD. If you don't do anything, it'll go to the hard drive to boot.
That's how it's supposed to work to avoid the endless installation process. Then again, if the user intervenes and keeps clicking "yes" to boot from the cd instead of just letting the option time out and go to the hard drive, then...

But there should be no reason to have to adjust boot priority in bios.