Xfce4-panel plugins unable to be themed by Xfce widgets and classes

There is a README in the source code at xfce4-panel-4.11.0/docs/README.gtkrc-2.0 which you can read at https://github.com/EasternHeart/heartlenv-panel/blob/master/docs/README.gtkrc-2.0 - it explains how to theme various aspects of the panel.

NONE of those which declare a perimeter in gtk-icon-sizes work:

XfceApplicationsMenuPlugin
XfceDirectoryMenuPlugin
XfceWindowMenuPlugin
XfceLauncherPlugin
XfceTasklist
XfceActionsPlugin

For example, placing the following in to $HOME/.gtkrc-2.0 results in no changes.

gtk-icon-sizes="panel-tasklist-menu=64,64"

style "xfce-tasklist-style"
{
  XfceTasklist::max-button-size = 64
}
class "XfceTasklist" style "xfce-tasklist-style"

I am sure that $HOME/.gtkrc-2.0 *is* being read because other parts of the file have effect.

Since xsettings.xml is no longer used to increase these sizes on the panel, this means that it is not possible to increase any panel menu icons sizes above the tiny 16 pixel size. This effectivle blocks many visually impaired people from using Xfce.

As I am trying to build a distro based on Xfce, I'd be very, very appreciative of a fix. :-)

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: xfce4-panel 4.11.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9
Uname: Linux 3.13.0-24-generic x86_64
ApportVersion: 2.14.1-0ubuntu3
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Apr 26 22:04:34 2014
InstallationDate: Installed on 2014-04-26 (0 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: xfce4-panel
UpgradeStatus: No upgrade log present (probably fresh install)