When thinking some more about when it change in behaviour happened, I realised that the freeze started about 2 weeks ago, so it could very well be related to that. It looks like the "apt-config dump" interpreted /etc/apt/apt.conf correctly, but in case the format of that file is relevant, here's the content of that file: Apt { Default-Release "testing"; Install-Recommends "0"; }; Aptitude { Autoclean-After-Update "true"; };