Here is a better fix, which won't be undone when unity next updates.
dpkg-divert --local --rename --divert /usr/share/unity/5/panel-shadow.png_disabled --add /usr/share/unity/5/panel-shadow.png
Here is a better fix, which won't be undone when unity next updates.
dpkg-divert --local --rename --divert /usr/share/ unity/5/ panel-shadow. png_disabled --add /usr/share/ unity/5/ panel-shadow. png