/usr/share/doc/libqt4-designer-dbg/changelog.Debian.gz is in libqt4-designer-dbg 4:4.8.7+dfsg-7ubuntu1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/doc/libqt4-designer-dbg/../libqtcore4/changelog.Debian.gz