We seem to be running into an issue with the existing xfce4-panel-4.8.3-2.el6. We seem to have the panel kernel panic crash seeming related to xfce4-panel (homedir NFS + panel operation + andmaybe Xen = random crash) on a fully updated CentOS 6.4. A couple of the (likely) related bugs with the xfce4-panel-4.8.x era version include:
https://bugzilla.redhat.com/show_bug.cgi?id=827508
https://bugzilla.xfce.org/show_bug.cgi?id=7951