debootstrap fails

[Gaël DONVAL <gael.donval@cnrs-imn.fr>]

Hi all,

I try to install Debian from my Debian onto an external SSD disk. 
The SSD disk is plugged on a USB3 dock.
The partition to be used for the installation is a BTRFS one.
The BTRFS partition is mounted with the following options:
rw,noatime,compress=lzo,ssd,space_cache,uhelper=udisks

When I try to use debootstrap on the internal HDD, everything works just
fine.

When I try to use debootstrap on the external SSD, it fails:

[...]
I: Extracting liblzma5...
I: Extracting xz-utils...
I: Extracting zlib1g...
I: Installing core packages...
W: Failure trying to run: chroot /media/System_/__root dpkg
--force-depends
--install /var/cache/apt/archives/base-files_6.9_amd64.deb /var/cache/apt/archives/base-passwd_3.5.26_amd64.deb
W: See /media/System_/__root/debootstrap/debootstrap.log for details


debootstrap.log:
gpgv: Signature made Fri Aug 24 22:19:23 2012 CEST using RSA key ID
473041FA
gpgv: Good signature from "Debian Archive Automatic Signing Key
(6.0/squeeze) <ftpmaster@debian.org>"
dpkg: warning: parsing file '/var/lib/dpkg/status' near line 5 package
'dpkg':
 missing description
dpkg: warning: parsing file '/var/lib/dpkg/status' near line 5 package
'dpkg':
 missing architecture
dpkg: unrecoverable fatal error, aborting:
 syntax error: unknown user 'root' in statoverride file


Allow me to remind you that everything works just fine on my internal
hdd.

Any idea?