Running the control center raises the following errors:

~> gnome-control-center

** (gnome-control-center:24705): CRITICAL **: Could not build interface: Unhandled tag: 'style'

(gnome-control-center:24705): Gtk-CRITICAL **: gtk_window_set_application: assertion `GTK_IS_WINDOW (window)' failed

(gnome-control-center:24705): Gtk-CRITICAL **: gtk_bin_get_child: assertion `GTK_IS_BIN (bin)' failed

(gnome-control-center:24705): Gtk-CRITICAL **: gtk_widget_show_all: assertion `GTK_IS_WIDGET (widget)' failed

(gnome-control-center:24705): Gtk-CRITICAL **: gtk_window_present_with_time: assertion `GTK_IS_WINDOW (window)' failed

It seems to refer to the style tag used in shell/shell.ui. Dropping the tag solves the error.

Simple patch:

diff --git a/shell/shell.ui b/shell/shell.ui
index d6c19f3..b1c79d9 100644
--- a/shell/shell.ui
+++ b/shell/shell.ui
@@ -13,9 +13,6 @@
         <child>
           <object class="GtkToolbar" id="toolbar1">
             <property name="visible">True</property>
-            <style>
-              <class name="primary-toolbar"/>
-            </style>
             <child>
               <object class="GtkToolItem" id="toolbutton1">
                 <property name="visible">True</property>