Comment 100 for bug 1642966

The root cause of this problem is probably that the "invoke-rc.d cups stop" command fails on Xenial if there are jobs in queue. The dpkg preremoval script runs that command and thus the upgrade procedure fails. In the newer Ubuntu versions the command executes flawlessly.

Until that problem is fixed in some way or another in Xenial, it isn't probably possible at all to safely publish any updates to cups-daemon, not even critical zero-day security patches.