Echec Debian dist-upgrade testing

  Bonjour,

Nouvel upgrade de jessie à testing... mais encore un soucis d'espace
disque sur "/" et "/var" en cours d'opération. Résultat:

> sudo apt-get upgrade
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer
required:
 [....]
Use 'sudo apt autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1582 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
N: Ignoring file 'debian-jessie-backports.list.backup' in directory
'/etc/apt/sources.list.d/' as it has an invalid filename extension
Do you want to continue? [Y/n] y
apt-listchanges: APT_HOOK_INFO_FD environment variable is incorrectly
defined
(Dpkg::Tools::Options::/usr/bin/apt-listchanges::InfoFD should be
greater than 2).
W: No sandbox user '_apt' on the system, can not drop privileges
E: Sub-process /usr/bin/apt-listchanges --apt || test $? -ne 10
returned an error code (1)
E: Failure running script /usr/bin/apt-listchanges --apt || test $? -ne
10

Donc 1500 packets non complètement configurés et toute commande APT qui
échoue avec ce message d'erreur de apt-listchanges

Comment corriger ce problème de variable APT_HOOK_INFO_FD et
d'utilisateur "_apt" manquant pour poursuivre ?

D'avance merci pour votre aide
-- 
Yves Martin