I'm currently trying to build a sid chroot, and it's failing with the
following error:

D: call action: apt-install
D: Execute "apt-get install --yes -o APT::Get::AllowUnauthenticated=true -o
APT::Install-Recommends=false libc-dev-bin linux-libc-dev
 libc6-dev libgmp3c2 libmpfr1ldbl cpp-4.4 cpp binutils libgomp1 gcc-4.4 gcc
g++-4.4 libstdc++6-4.4-dev g++ make libdb4.7 libgdbm3 per
l perl-modules bzip2 liblzma2 xz-utils patch libtimedate-perl dpkg-dev
build-essential fakeroot" in chroot
O: Reading package lists...
O:
O: Building dependency tree...
O:
O: Suggested packages:
O:   binutils-doc bzip2-doc cpp-doc gcc-4.4-locales debian-keyring
O:   debian-maintainers g++-multilib g++-4.4-multilib gcc-4.4-doc
O:   libstdc++6-4.4-dbg gcc-multilib manpages-dev autoconf automake1.9 libtool
O:   flex bison gdb gcc-doc gcc-4.4-multilib libmudflap0-4.4-dev libgcc1-dbg
O:   libgomp1-dbg libmudflap0-dbg libcloog-ppl0 libppl-c2 libppl7 glibc-doc
O:   libstdc++6-4.4-doc make-doc ed diffutils-doc perl-doc
O:   libterm-readline-gnu-perl libterm-readline-perl-perl
O: Recommended packages:
O:   netbase
O: The following NEW packages will be installed:
O:   binutils build-essential bzip2 cpp cpp-4.4 dpkg-dev fakeroot g++ g++-4.4 gcc
O:   gcc-4.4 libc-dev-bin libc6-dev libdb4.7 libgdbm3 libgmp3c2 libgomp1 liblzma2
O:   libmpfr1ldbl libstdc++6-4.4-dev libtimedate-perl linux-libc-dev make patch
O:   perl perl-modules xz-utils
O: 0 upgraded, 27 newly installed, 0 to remove and 0 not upgraded.
O: Need to get 0B/33.0MB of archives.
O: After this operation, 106MB of additional disk space will be used.
O: WARNING: The following packages cannot be authenticated!
O:   libgdbm3 libdb4.7 patch perl-modules perl binutils libc-dev-bin
O:   linux-libc-dev libc6-dev libgmp3c2 libmpfr1ldbl cpp-4.4 cpp libgomp1 gcc-4.4
O:   gcc libstdc++6-4.4-dev g++-4.4 g++ make bzip2 liblzma2 xz-utils
O:   libtimedate-perl dpkg-dev build-essential fakeroot
O: Authentication warning overridden.
O: Err bootstrap: ./main libtimedate-perl 1.2000-1
O:
O: Failed to fetch
bootstrap:/pool/main/libt/libtimedate-perl/libtimedate-perl_1.2000-1_all.deb

This would be because cdebootstrap earlier downloaded a different version of
libtimedate-perl:

P: Retrieving libtimedate-perl
D: Execute "wget -q -O
/tmp/cdebootstrap/var/cache/bootstrap/libtimedate-perl_1.1900-1_all.deb
http://localhost:9999/debian/pool/main
/t/timedate/libtimedate-perl_1.1900-1_all.deb"

Discussions on #debian-devel suggested that at present, there are two
versions of libtimedate-perl in unstable because a different source package
got uploaded.  Whilst this problem can be fixed by cleaning up the archive,
it seems to me that cdebootstrap could handle this case better -- presumably
by picking the same version of the package that apt would.