Comment 4 for bug 842179

I've traced this issue to a value in /root/.synaptic/synaptic.conf :

Synaptic "" {
  ViewMode "3";
  showWelcomeDialog "0";
  LastSearchType "1";
  closeZvt "true";
  vpanedPos "214";
  hpanedPos "152";
  windowWidth "1280";
  windowHeight "947";
  windowX "0";
  windowY "30";
  ToolbarState "2";
  Maximized "1";
  Install-Recommends "1";
  AskForUpdateAfterSrcChange "0";
  update "" {
    last "1316901731";
    type "0";
  };

  ShowAllPkgInfoInMain "true";
  AskRelated "true";
  OneClickOnStatusActions "false";
  delAction "3";
  upgradeType "1";
  undoStackSize "20";
  UseTerminal "false";
  AskQuitOnProceed "false";
  useUserFont "0";
  useUserTerminalFont "0";
  statusColumnPos "0";
  statusColumnVisible "1";
  supportedColumnPos "1";
  supportedColumnVisible "1";
  nameColumnPos "2";
  nameColumnVisible "1";
  sectionColumnPos "3";
  sectionColumnVisible "0";
  componentColumnPos "4";
  componentColumnVisible "0";
  instVerColumnPos "5";
  instVerColumnVisible "1";
  availVerColumnPos "6";
  availVerColumnVisible "1";
  instSizeColumnPos "7";
  instSizeColumnVisible "1";
  downloadSizeColumnPos "8";
  downloadSizeColumnVisible "0";
  descrColumnPos "9";
  descrColumnVisible "1";
  color-install "#8A8AE2E23434";
  color-reinstall "#4E4E9A9A0606";
  color-upgrade "#FCFCE9E94F4F";
  color-downgrade "#ADAD7F7FA8A8";
  color-remove "#EFEF29292929";
  color-purge "#A4A400000000";
  color-available "";
  color-available-locked "#A4A400000000";
  color-installed-updated "";
  color-installed-outdated "";
  color-installed-locked "#A4A400000000";
  color-broken "";
  color-new "";
  UseStatusColors "true";
  CleanCache "false";
  AutoCleanCache "true";
  delHistory "-1";
  useProxy "0";
  httpProxy "";
  httpProxyPort "3128";
  ftpProxy "";
  ftpProxyPort "3128";
  noProxy "";
  DefaultDistro "maverick";
};

The bit with DefaultDistro "maverick"; was causing this issue for me.
For a quick one line solution you can run the following command:

release=`lsb_release -a 2>1| grep Codename| awk '{print $2}'`;for file in /root/.synaptic/synaptic.conf $HOME/.synaptic/synaptic.conf ; do sudo sed -i "s/DefaultDistro \".*;/DefaultDistro \"$release\";/g" $file; done;