Comment 3 for bug 1428571

Just got the same issue. Performed the following tests, just to get out of this :
- first, install updates from GUI; failed, it hangs forever. I had to kill all apt-get process
- second, apt-get update then apt-get upgrade. After the upgrade, triggers, then the configure mysql-apt-config, but with the console menu.

> ps -aux | grep apt | grep -v 'grep'
root 3422 53.7 5.3 424336 218008 ? SNl 20:11 15:59 /usr/bin/python3 /usr/sbin/aptd
root 5050 0.0 0.0 83784 2224 ? S 20:33 0:00 sudo apt-get upgrade
root 5051 4.8 1.3 101724 55200 ? S 20:33 0:22 apt-get upgrade
root 5673 0.0 0.1 26024 7996 pts/1 Ss+ 20:34 0:00 /usr/bin/dpkg --status-fd 83 --configure mysql-apt-config:all compiz-core:amd64 libcompizconfig0:amd64 libdecoration0:amd64 compiz-plugins-default:amd64 compiz-gnome:amd64 compiz-plugins:amd64 compiz:all unity-services:amd64 libunity-core-6.0-9:amd64 unity:amd64 compiz-plugins-extra:all python-compizconfig:amd64 compizconfig-settings-manager:all
root 5676 0.0 0.3 67644 14288 pts/1 S+ 20:34 0:00 /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/mysql-apt-config.postinst configure 0.3.2-1ubuntu14.04
root 5682 0.0 0.0 16768 1432 pts/1 S+ 20:34 0:00 /bin/bash /var/lib/dpkg/info/mysql-apt-config.config configure 0.3.2-1ubuntu14.04
root 5794 0.0 0.0 25384 2276 pts/1 S+ 20:41 0:00 whiptail --backtitle Outil de configuration des paquets --title Configuration de mysql-apt-config --output-fd 11 --nocancel --default-item mysql-5.6 --menu This configuration program will detect the current state of your system, check for any installed MySQL Server packages, and try to select the most appropriate version of MySQL Server to be installed. If you are not sure which version to choose for yourself, do not change the auto-selected version. Advanced users can always change the version later, depending on their own needs. Which server version do you wish to receive? 14 208 3 -- mysql-5.6 mysql-5.7-dmr none

Then, I tried to kill the menu process (5794) itself : comes back (probably from another process). Then tried the process mysql-apt-configure (5682) without killing neither the process apt-get upgrade nor dpkg (which contained all triggers and the state). Process came with a malfunc, GUI show me the classic "Report bug" window. The next apt-get upgrade does not show me any package, but I think I simply cleaned apt... until next update.
Mysql works fine too.

If it could help anyone...