RH9 automagically mounts, but you have to specifically tell it to unmount before ejecting ?
Or maybe - I've noticed that if I browse a mounted CD with Konqueror (KDE 3.3.2 and earlier), it starts a kio_thumbnail process. I cant eject the disk until the process is killed. Usually by closing the konqueror window. This happens with both Mandrake 10.1 and Slackware 10. Mandrake should automagically mount and umount the disk, using supermount, but the kio_thumbnail process blocks this. Slackware needs me to manually mount and unmount, it the CD is mounted, then no amount of button pressing ejects it.
Try a manual 'umount /mnt/media' before pressing the eject button.