It seems that my unstable chroot is broken. When I do an upgrade, I get this error message

E: dpkg was interrupted, you must manually run 'dpkg --configure -a' to correct the problem. 
/srv/chroot/unstable-i386-sbuild has Operating System (Debian Unstable) "i386" ... ok
/srv/chroot/unstable-i386-sbuild noop property ... ok
/srv/chroot/unstable-i386-sbuild apt installed apt-transport-https ... ok
/srv/chroot/unstable-i386-sbuild standard sources.list ... ok
Hit:1 http://ftp2.fr.debian.org/debian unstable InRelease
Hit:2 http://mirrors.kernel.org/debian unstable InRelease
/srv/chroot/unstable-i386-sbuild apt update ... failed
/srv/chroot/unstable-i386-sbuild apt cache cleaned ... ok
mordor chroot /srv/chroot/unstable-i386-sbuild provisioned ... failed

the properties are here sbuild :: System -> Proxy -> RevertableProperty HasInfo sbuild system proxy = Sbuild.schroot schrootname chroot where chroot = Chroot.debootstrapped Debootstrap.BuilddD chrootdir & os system & case proxy of (Just p) -> "/etc/apt/apt.conf.d/01proxy" File.hasContent ["Acquire::http::Proxy \"" ++ p ++ "\";"] Nothing -> doNothing & Apt.installed ["apt-transport-https"] & Apt.stdSourcesList & Apt.update onChange Apt.upgrade & Apt.cacheCleaned schrootname = Sbuild.schrootname system chrootdir = "/srv/chroot" schrootname

so the update failed and the solution seems to be

dpkg --configure -a

Is it possible to deal with this problem in the update property in order to make it transparent for the users.