Comment 50 for bug 1727355

On a xenial server, with distro-info-data 0.28ubuntu0.6 from current xenial-updates, juju-core is removed:
     0.28ubuntu0.6 500
        500 http://archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages

root@atlas:~# apt install distro-info-data
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
  juju-core
The following packages will be upgraded:
  distro-info-data
1 upgraded, 0 newly installed, 1 to remove and 129 not upgraded.

Enabling xenial-proposed and retrying, it installs just fine and juju-core is kept:
     0.28ubuntu0.7 500
        500 http://archive.ubuntu.com/ubuntu xenial-proposed/main amd64 Packages

root@atlas:~# apt install distro-info-data
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be upgraded:
  distro-info-data
1 upgraded, 0 newly installed, 0 to remove and 171 not upgraded.
Need to get 0 B/4,334 B of archives.
After this operation, 0 B of additional disk space will be used.
(Reading database ... 154932 files and directories currently installed.)
Preparing to unpack .../distro-info-data_0.28ubuntu0.7_all.deb ...
Unpacking distro-info-data (0.28ubuntu0.7) over (0.28ubuntu0.5) ...
Setting up distro-info-data (0.28ubuntu0.7) ...