apt-clone: "Could not exec dpkg"

I tried to restore the apt-clone state file from bug 922485 into a chroot so that I could investigate it, running it as 'sudo http_proxy=http://wwwcache:3142/ linux32 apt-clone restore --destination /media/passport/chroot/lucid-precise-922485 ./922485-apt-clone_system_state.tar.gz'. The restore eventually failed with:

  Chrooting into /media/passport/chroot/lucid-precise-922485/
  Could not exec dpkg!

strace shows that the execve call is:

  17145 execve("/media/passport/chroot/lucid-precise-922485/usr/bin/dpkg", ["/media/passport/chroot/lucid-precise-922485/usr/bin/dpkg", "--status-fd", "16", "--unpack", "--auto-deconfigure", "/var/cache/apt/archives/libpam-modules_1.1.1-2ubuntu5.4_i386.deb"], [/* 22 vars */] <unfinished ...>

That shouldn't have the chroot directory prefixed. I don't know whether this is a bug in apt-clone or in apt.

I've attached a bzipped strace of the tail-end of the apt-clone run.