Boot fails with remastered ubuntu CD

[Josef Wolf]

Hello!

I am trying to create a customized ubuntu install CD based on edgy
alternate install CD as described on

  https://help.ubuntu.com/community/InstallCDCustomization

Basically, what I am trying to do is:

  mkdir -p mnt
  sudo mount -oro,loop /downloads/ubuntu-6.10-alternate-i386.iso mnt
  cp -rT mnt custom
  chmod -R u+w custom
  sudo umount mnt
  mkisofs -r -V 'My Install CD' -cache-inodes -J -l \
      -b isolinux/isolinux.bin -c isolinux/boot.cat -no-emul-boot \
      -boot-load-size 4 -boot-info-table -o custom.iso custom
  sudo nice -18 cdrecord blank=fast -eject -v gracetime=2 -tao custom.iso

With this, I get a working CD, thus I think I've got the basics right.
But when I do the slightest modification to the isolinux.cfg, the
generated CD hangs just after presenting the ubuntu splash screen even
before the boot menu is presented.  For example, even the following
modification will cause the CD to hang:

--- custom/isolinux/isolinux.cfg.orig   2006-11-30 17:21:51.000000000 +0100
+++ custom/isolinux/isolinux.cfg        2006-11-30 17:22:27.000000000 +0100
@@ -3,7 +3,7 @@
 GFXBOOT-BACKGROUND 0xB6875A
 APPEND  file=/cdrom/preseed/ubuntu.seed initrd=/install/initrd.gz ramdisk_size=16384 root=/dev/ram rw quiet --
 LABEL install
-  menu label ^Install in text mode
+  menu label ^Gem install
   kernel /install/vmlinuz
   append  file=/cdrom/preseed/ubuntu.seed initrd=/install/initrd.gz ramdisk_size=16384 root=/dev/ram rw quiet --
 LABEL linux

Any ideas what's going wrong here?  What does the caret in the
"menu label" line mean?  The syslinux/isolinux documentation don't even
mention that a "menu label" line exists.  Does ubuntu use a modified
version of isolinux?