I've successfully downgraded most of my system from unstable to jessie, so this seems to be workable.
Among the things I run, there's only MySQL that can't be downgraded just like that from unstable's 5.6 to jessie's 5.5, and for which there is no backport of 5.6; and also libstdc++6 that I can't downgrade from GCC 5 to GCC 4.9 because mysql binaries depend on it. An unsupported MySQL server is a nice attack vector. Is that kind of downgrade supposed to be supported? I encountered configuration migration problems for apt and postfix, shall I file bugs for these? I still think this bug should be marked as wontfix because "enjoy 4 years of jessie" is not a real fix to the problem. Thanks for the guidance, -- Pierre Ynard "Une âme dans un corps, c'est comme un dessin sur une feuille de papier."