Comment 8 for bug 1639558

Unattended-upgrade uses ufc(1) to manage the related conffiles and ucf creates those copies during the update.

Starting with u-u 1.4 README.md recommends creating separate configuration files in /etc/apt/apt.conf.d to avoid updates to conflict with local changes.

Latest apt ignores the .ucf-* files which is the right thing IMO and either giving warning or not giving a warning is OK on apt's side.