I don't understand why your /dev/hde1 would be mounted as /cdrom, even your original fstab has it mounting as /mnt/hde1
OK, I did more testing and discovered that /cdrom is being used as the mount point because I'm using the fromhd=/dev/hde1 cheat code.

If I don't use this cheat code and let knoppix load from the CD, then that becomes /cdrom. /dev/hde1 is not mounted at all, but I can do a "mount -a" and then it will be mounted rw. Note: this behaviour is the same whether or not the auto option is in the fstab for /dev/hde1

Using the fromhd cheat code mounts /dev/hde1 as /cdrom. (This must be necessary to load the image, since /cdrom does not appear in the fstab). Doing a "mount -a" at this point fails because the device is already mounted.

Of course, I want to run with the cheat code for performance reasons. Is there any way to do this?