Comment 8 for bug 650525

One possible fix is:
=== modified file 'livecd.sh'
--- livecd.sh 2010-09-24 12:54:11 +0000
+++ livecd.sh 2010-09-30 09:37:01 +0000
@@ -504,8 +504,7 @@

     # In addition to the ones we got from apt, trust whatever the local system
     # believes in, but put things back afterwards.
- cp ${ROOT}etc/apt/trusted.gpg ${ROOT}etc/apt/trusted.gpg.$$
- cat /etc/apt/trusted.gpg >> ${ROOT}etc/apt/trusted.gpg
+ cp /etc/apt/trusted.gpg ${ROOT}etc/apt/trusted.gpg.d/build-host.gpg

     chroot $ROOT apt-get update
     checkpoint "Upgrading"
@@ -645,7 +644,8 @@
 Pin-Priority: 550
 @@EOF
     fi
- mv ${ROOT}etc/apt/trusted.gpg.$$ ${ROOT}etc/apt/trusted.gpg
+ # remove the keys from the build host again
+ rm ${ROOT}etc/apt/trusted.gpg.d/build-host.gpg

     # get rid of the .debs - we don't need them.
     chroot ${ROOT} apt-get clean