Need advice about a package installing no files at all

[Emmanuel Kasper <emmanuel@libera.cc>]

Hello

After doing an upgrade from debian 6 to 7, the packge xmess-sdl is list
as installed but does not contains any file at all.
( http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=685470 )

(s2w)root@dakar:/# dpkg -L xmess-sdl
/.
/usr
/usr/share
/usr/share/doc
/usr/share/doc/xmess-sdl
/usr/share/doc/xmess-sdl/changelog.Debian.gz
/usr/share/doc/xmess-sdl/changelog.gz
/usr/share/doc/xmess-sdl/copyright

(s2w)root@dakar:/# cat /usr/share/doc/xmess-sdl/copyright
cat: /usr/share/doc/xmess-sdl/copyright: No such file or directory
(s2w)root@dakar:/#

I don't see anything suspicious in /var/log/dpkg.log, I have no clues
about what could cause that or where to get a debug mode. Where shoud I
look for ?

Emmanuel