When a CD is inserted and mounted, right-clicking its icon shows an "Eject" command but "Unmount" is missing. If the CD is unmounted, right-clicking its icon shows a "Mount" command but "Eject" is missing.
I don't intend to allow unmount while the CD is mounted. Eject should be the only option. You're right, though, it should have an Eject option as well when it's unmounted. Not a big deal for now, though: can just mount and then eject for the time being.
Fixed in trunk and 4.6 branch.