apt-get, похоже, игнорирует указанные версии пакета

Я просто добавил PPA (для Compiz) с более низкими номерами версий и сделал файл apt_preferences:

Package: *
Pin: release o=LP-PPA-townsend-compiz-nvidia-refresh-test
Pin-Priority: 600

Конечно, политики были изменены, но мне нужно «понизить» пакеты на (здесь я уже сделал это с compiz):

$ apt-cache policy libcompizconfig0 compiz{,-core,-gnome,config-settings-manager,-plugins{,-default}}  
libcompizconfig0:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
compiz:
  Installed: 1:0.9.11+14.04.20140423-0ubuntu1ppa2
  Candidate: 1:0.9.11+14.04.20140423-0ubuntu1ppa2
  Version table:
     1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
 *** 1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
compiz-core:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
compiz-gnome:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages
compizconfig-settings-manager:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/universe amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/universe amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/universe amd64 Packages
compiz-plugins:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/universe amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/universe amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/universe amd64 Packages
compiz-plugins-default:
  Installed: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Candidate: 1:0.9.11.1+14.04.20140623-0ubuntu1
  Version table:
 *** 1:0.9.11.1+14.04.20140623-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     1:0.9.11+14.04.20140423-0ubuntu1ppa2 0
        600 http://ppa.launchpad.net/townsend/compiz-nvidia-refresh-test/ubuntu/ trusty/main amd64 Packages
     1:0.9.11+14.04.20140423-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty-updates/main amd64 Packages
     1:0.9.11+14.04.20140409-0ubuntu1 0
        500 http://archive.ubuntu.com/ubuntu/ trusty/main amd64 Packages

Вот что происходит, когда я пытаюсь сразу заменить версии из PPA:

$ sudo apt-get install  {libcompizconfig0,compiz{,-core,-gnome,config-settings-manager,-plugins{,-default}}}=1:0.9.11+14.04.20140423-0ubuntu1ppa2
Reading package lists... Done
Building dependency tree       
Reading state information... Done
compiz is already the newest version.
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 compiz-plugins : Depends: compiz-core (= 1:0.9.11.1+14.04.20140623-0ubuntu1) but 1:0.9.11+14.04.20140423-0ubuntu1ppa2 is to be installed
 compiz-plugins-default : Depends: compiz-core (= 1:0.9.11.1+14.04.20140623-0ubuntu1) but 1:0.9.11+14.04.20140423-0ubuntu1ppa2 is to be installed
E: Unable to correct problems, you have held broken packages.

Что это о требовании 1:0.9.11.1+14.04.20140623-0ubuntu1? Я указал совместимые версии для всех пакетов.

Давайте попробуем что-нибудь более консервативное:

$ sudo apt-get install  compiz-core=1:0.9.11+14.04.20140423-0ubuntu1ppa2
Reading package lists... Done
Building dependency tree   
Reading state information... Done
The following packages will be REMOVED:
  compiz compiz-gnome compiz-plugins compiz-plugins-default
  compizconfig-settings-manager libcompizconfig0 python-compizconfig
  ubuntu-desktop unity unity-tweak-tool
The following packages will be DOWNGRADED:
  compiz-core
0 upgraded, 0 newly installed, 1 downgraded, 10 to remove and 1 not upgraded.
Need to get 710 kB of archives.
After this operation, 24.7 MB disk space will be freed.
Do you want to continue? [Y/n] n
Abort.

Хорошо, это не сработает. По-видимому, попытка «понизить» любую комбинацию соответствующих пакетов приведет к тому же «сломанным пакетам».

На данный момент у меня нет идей.