## Step to reproduce

Fresh intallation with guix-system-install-1.4.0rc1.x86_64-linux.iso
guix pull
guix package -u
sudo guix system reconfigure /etc/config.scm

## Expected result

the system is upgraded

** Unexpected result

guix system: erreur : aborting reconfiguration because commit
d7c8cb7e53682a52a80bd35e2deaaab7f3e0c912 of channel 'guix' is not a
descendant of 883fefe1605499c8d98426f2915816dddd7448ef
conseil : Utilisez `--allow-downgrades' pour forcer ce retour en
arrière.

## Note:
I did the installation twice with the same result, once with guix
package -u once without guix package -u before guix system reconfigure

Hardware:
Lenovo T400 with libreboot
Intel core T9900 × 2
sda /
sdb /home (encrypted)