Comment 10 for bug 172879

I've made some progress here on the obvious underlying issues. In debconf:

  * debconf-apt-progress: If we get cancelled very early on before managing
    to start the process we're controlling, make sure that we don't carry on
    and start it anyway, and that we still return 30.
  * debconf-apt-progress: Handle cancellation right at the end. We don't
    have a process to kill at this point, but we should at least return the
    correct exit code.

... and in debian-installer-utils:

  * Change in-target and apt-install to pass through non-zero exit codes
    unmolested rather than collapsing them to 1. In particular, this allows
    cancellation exit codes from debconf-apt-progress to be detected by
    apt-setup (see
    http://lists.debian.org/debian-boot/2008/01/msg00094.html).

I'll see how well things work when these changes make their way into Ubuntu installer builds.