Why is apt-get ignoring the target argument?

My Debian system is set to install unstable packages by default $ cat /etc/apt/apt.conf.d/99defaultrelease APT::Default-Release "unstable"; However, I would like to pull automake from stable, ie, version 1.15 $ apt-cache policy automake automake: Installed: (none) Candidate: 1:1.16.1-4 Version table: 1:1.16.1-4 990 500 http://deb.debian.org/debian testing/main amd64 Packages 500 http://deb.debian.org/debian testing/main i386 Packages 990 http://deb.debian.org/debian unstable/main amd64 Packages 990 http://deb.debian.org/debian unstable/main i386 Packages 990 http://deb.debian.org/debian sid/main amd64 Packages 990 http://deb.debian.org/debian sid/main i386 Packages 1:1.15-6 500 500 http://deb.debian.org/debian stable/main amd64 Packages 500 http://deb.debian.org/debian stable/main i386 Packages But whenever I tell it to install automake/stable or automake with -t stable, apt just ignores that part. $ apt-get install automake -t stable --dry-run Reading package lists... Done Building dependency tree Reading state information... Done The following additional packages will be installed: autoconf autotools-dev Suggested packages: autoconf-archive gnu-standards autoconf-doc libtool The following NEW packages will be installed: autoconf automake autotools-dev 0 upgraded, 3 newly installed, 0 to remove and 125 not upgraded. Inst autoconf (2.69-11 Debian:testing, Debian:unstable [all]) Inst autotools-dev (20180224.1 Debian:testing, Debian:unstable [all]) Inst automake (1:1.16.1-4 Debian:testing, Debian:unstable [all]) Conf autoconf (2.69-11 Debian:testing, Debian:unstable [all]) Conf autotools-dev (20180224.1 Debian:testing, Debian:unstable [all]) Conf automake (1:1.16.1-4 Debian:testing, Debian:unstable [all]) I can specify the package version like this: apt-get install automake=1:1.15-6 Which should solve my problem, although the dependencies (autoconf, autotools-dev, etc.) will still be installed from unstable, which is a little concerning. Anyway why is apt ignoring the given target in this case? Also - this is not a question - if this behavior is "by design", I think it would be really nice if apt could print some informative notice. ## Edit This is the output of apt -t stable policy automake (note: *after* having installed automake) $ apt -t stable policy automake automake: Installed: 1:1.16.1-4 Candidate: 1:1.16.1-4 Version table: *** 1:1.16.1-4 1001 500 http://deb.debian.org/debian testing/main amd64 Packages 500 http://deb.debian.org/debian testing/main i386 Packages 1001 http://deb.debian.org/debian unstable/main amd64 Packages 1001 http://deb.debian.org/debian unstable/main i386 Packages 1001 http://deb.debian.org/debian sid/main amd64 Packages 1001 http://deb.debian.org/debian sid/main i386 Packages 100 /var/lib/dpkg/status 1:1.15-6 990 990 http://deb.debian.org/debian stable/main amd64 Packages 990 http://deb.debian.org/debian stable/main i386 Packages Since this might be an issue with priorities, this might also be relevant: $ cat /etc/apt/preferences Package: * Pin: release a=unstable Pin-Priority: 1001