DRAW-INVERTED-PINBOARD-OBJECT dies when object has custom background and foreground

Hi does anybody have a workaround for this?

======================================================================== 
===============
(defun make-colored-node (gp item)
   (make-instance 'capi:expandable-item-pinboard-object
                  :text (format nil "~A" item)))

(defun children-f (i)
   (when (< i 20)
     (list (* i 2)
           (1+ (* i 2)))))

(defparameter gp (capi:contain (make-instance 'capi:graph-pane
                                               :visible-min-width 300
                                               :visible-min-height 300
                                               :node-pane-function
'make-colored-node
                                               :roots '(1 2 3 42)
                                               :children-function
'children-f
                                               )))


(defun modify-colors (gp)
   (let ((vs (capi:graph-pane-nodes gp)))
     (dolist (v vs)
       (let ((e (capi:graph-object-element v))
             (o (capi:graph-object-object v))
             )
         (when (oddp o)
           (setf (capi:pinboard-object-graphics-arg e :background)
:cyan))))))

======================================================================== 
===============

Evaluate the code and then issue

	(modify-colors gp)

at the listener.

If you select (collapse or expand) a EVENP node everything works as  
expected.
If you select (collapse or expand) a ODDP node  
DRAW-INVERTED-PINBOARD-OBJECT dies badly.

I need a way to color the nodes while keeping the expand/collapse of  
the nodes in the graph pane working.
This is a show-stopper for me now.

Cheers

--
Marco Antoniotti					http://bioinformatics.nyu.edu/~marcoxa
NYU Courant Bioinformatics Group		tel. +1 - 212 - 998 3488
715 Broadway 10th FL				fax. +1 - 212 - 998 3484
New York, NY, 10003, U.S.A.