APT pinning fails

acolomb@multilus:/etc/apt$ cat preferences
Explanation: Only install package updates from deb-multimedia.org manually
Package: *
Pin: release l="Unofficial Multimedia Packages"
Pin-Priority: 99
acolomb@multilus:/etc/apt$ apt-cache policy libavcodec-dev
libavcodec-dev:
  Installed: 6:0.8.3-5
  Candidate: 7:0.11.1-dmo3
  Version table:
     7:0.11.1-dmo3 0
        990 http://ftp-stud.hs-esslingen.de/pub/Mirrors/debian-multimedia/ testing/main amd64 Packages
     6:0.8.99-1537-gacb2c79-2 0
          1 http://ftp.de.debian.org/debian/ experimental/main amd64 Packages
 *** 6:0.8.3-5 0
        500 http://ftp.de.debian.org/debian/ unstable/main amd64 Packages
        100 /var/lib/dpkg/status
     6:0.8.3-4 0
        990 http://ftp.de.debian.org/debian/ testing/main amd64 Packages
acolomb@multilus:/etc/apt$