Why doesn quickreboot (or some other boot parameter) work?
If you are building an etch image (which was the default up to 2007/09/14) you have a very old version of casper which does not support quickreboot and possibly other boot parameters as well. You could configure your sources to use live-backports (see /usr/share/live-helper/examples/sources/live-backports) and switch to live-initramfs, or better yet, build a lenny image instead, which is the new default.