More info about this. In my system, with unstable and the old libecm0 and gmp-ecm installed by hand (so they are "obsolete"):
# apt-get -s install gmp-ecm ... The following additional packages will be installed: libecm1 The following NEW packages will be installed: libecm1 The following packages will be upgraded: gmp-ecm 1 upgraded, 1 newly installed, 0 to remove and 145 not upgraded. Inst libecm1 (7.0+ds-1 Debian:unstable [amd64]) Inst gmp-ecm [6.4.4-2] (7.0+ds-1 Debian:unstable [amd64]) Conf libecm1 (7.0+ds-1 Debian:unstable [amd64]) Conf gmp-ecm (7.0+ds-1 Debian:unstable [amd64]) # apt-get -s upgrade ... The following packages have been kept back: gmp-ecm libecm0 # apt-get -s dist-upgrade ... The following NEW packages will be installed: libecm1 The following packages have been kept back: libecm0 The following packages will be upgraded: [...] gmp-ecm [...] So it seems that a direct request to install (upgrade) a package is always granted, even if libecm0 is left behind with unfulfilled recommends. Maybe it's because of being obsolete packages, unlike in the system where this originally happened. Cheers. -- Manuel A. Fernandez Montecelo <manuel.montez...@gmail.com>