Comment 8 for bug 879218

Well, it seems that downgrade really break something: no further system upgrades are possible, because there's dependencies unable to be resolved when you downgrade the package. Take a look:

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jordi@ubuntu: /home/jordi $ sudo aptitude dist-upgrade
The following packages will be upgraded:
  aisleriot binutils gnome-system-monitor libgssapi-krb5-2 libgssapi-krb5-2 libk5crypto3
  libk5crypto3 libkrb5-3 libkrb5-3 libkrb5support0 libkrb5support0 libunity-core-4.0-4
  libvlc-dev libvlc5 libvlccore-dev libvlccore4 unity unity-common unity-services vlc vlc-data
  vlc-nox vlc-plugin-notify vlc-plugin-pulse xserver-common xserver-xorg-core xserver-xorg-dev
27 packages upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
Need to get 21.3 MB of archives. After unpacking 20.5 kB will be used.
The following packages have unmet dependencies:
  compiz-plugins-main: Depends: compiz-plugins-main-default (= 1:0.9.6-0ubuntu4) but 1:0.9.6-0ubuntu2 is installed and it is kept back.
The following actions will resolve these dependencies:

       Remove the following packages:
1) appmenu-qt
2) compiz-plugins-main
...
138) vlc
139) zlib1g

       Leave the following dependencies unresolved:
140) indicator-appmenu recommends appmenu-qt
141) compizconfig-settings-manager recommends compiz-plugins-main
142) ia32-libs recommends ia32-libs-multiarch
143) virtualbox recommends libqt4-opengl (>= 4:4.5.3)
144) ubuntu-restricted-addons recommends flashplugin-installer

Accept this solution? [Y/n/q/?]
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So I don't recommend this unless you really know what you are doing.