The nomount option to 'linux rescue' should be documented on the help screens for the bootable CD. Nomount is the only way to rescue some systems: - anaconda crashes if fstab isn't consistent with partitions. I'd report a traceback, but it reboots right away. - rescue mounts all fses read-write, which is bad.
We are planning on prompting the user before attempting to mount the existing installation in our next release.