File names and backing up to DVD

[david-8uUts6sDVDvs2Lz0fTdYFQ at public.gmane.org (David Kramer)]

I usually back up to an external USB hard drive, but I'm playing with 
backing up to DVD, since I have a stack of DL dvds.  I threw together a 
quick script to call mkisofs, but I'm getting this:

Logfile is '/mnt/backup/dobackup.janus.20100123144543.out'
Backup file is '/mnt/backup/backups/backup.janus.20100123144543.iso'
Command is  'mkisofs -A dobackup.sh -v -l -J -R -L -V 
dkramer_backup_20100123144543 -o 
/mnt/backup/backups/backup.janus.20100123144543.iso
/boot /data/subversion /data2/subversion /etc /home /root /usr /var 
/backup/backup_mysql_janus_100123.tgz'
---------------------------------------------
Warning: creating filesystem that does not conform to ISO-9660.
I: -input-charset not specified, using utf-8 (detected in locale settings)
genisoimage 1.1.9 (Linux)
Scanning /boot
Scanning /boot/lost+found
Scanning /boot/grub
Scanning /data/subversion
...
Using PASSWD_000.;1 for  /passwd- (passwd~)
Using GROUP_000.;1 for  /group~ (group-)
Using 000.BASH_HISTORY;1 for  /.bash_history (.bash_history)
Using 001.BASH_HISTORY;1 for  /.bash_history (.bash_history)
Using 000.HTPASSWD;1 for  /.htpasswd (.htpasswd)

genisoimage: Error: '/data2/subversion/.htpasswd' and 
'/data/subversion/.htpasswd' have the same Rock Ridge name '.htpasswd'.
genisoimage: Error: '/var/mail' and '/etc/mail' have the same Rock Ridge 
name 'mail'.

Unable to sort directory
NOTE: multiple source directories have been specified and merged into 
the root of the filesystem. Check your program arguments. genisoimage is 
not tar.

Dunno what it's talking about with group and passwd, but the two naming 
conflicts puzzle me.  How can it complain about two files in completely 
different directories having the same name?

What's the best way around this?

If I only intend on using this on other Linux systems, would removing -J 
be enough, or are there more things to override?

Where are we going, and why are we in this handbasket?