We should use the new gnome-disk-image-mounter(1) command as the default for the application/x-cd-image MIME type instead of mount-archive.desktop The desktop file name is gnome-disk-image-mounter.desktop
Also, this new command is available in gnome-disk-utility-3.5.1-4.fc18
Will be in shared-mime-info-1.0-3.fc18
shared-mime-info-1.0-4.fc17 has been submitted as an update for Fedora 17. https://admin.fedoraproject.org/updates/shared-mime-info-1.0-4.fc17
shared-mime-info-1.0-4.fc17 has been pushed to the Fedora 17 stable repository. If problems still persist, please make note of it in this bug report.