/usr/share/doc/libstfl-ruby1.9.1/changelog.Debian.gz is in libstfl-ruby1.9.1 0.22-1.1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libstfl-ruby1.9.1/../libstfl-ruby/changelog.Debian.gz