/usr/lib64/xfce4/panel-plugins/datetime.desktop should be /usr/share/xfce4/panel-plugins/datetime.desktop
Sorry, but the file cannot be in %{_datadir}/xfce4/panel-plugins since it contains an arch specific path: X-XFCE-Module=datetime X-XFCE-Module-Path=/usr/lib64/xfce4/panel-plugins Because of the multilib issues we patched it to %{_libdir}/xfce4/panel-plugins and this was *your* idea, remember? ;) This is something that needs to be fixed upstream because it's a design issue with all external panel plugins. I already mentioned that while talking to Nick Schermer at FOSEDM this year in passing, but he did not see the problem.
Duh. This is what I get for doing about 5 things at once and offering to quickly file a bug for a #fedora user without thinking. ;) At least it was a quick bug to fix. ;)