The latest dpkg upgrade seems to have removed the force-overwrite
feature from apt, which is normally set in the unstable branch, but
removed when it comes to stable.
Add the lines:
DPkg
{
Options {"--force-overwrite";}
}
to the file /etc/apt/apt.conf (or create one if it don't exist).
And then file a bug for gnome-print.
Greetings,
joachim