Scroll-bar 'flashing' in divider layout

Hi,

I need to add scroll-bars to implement custom scrolling on two output-panes with
a divider, as in the following rudimentary example - 
   
(define-interface test ()
  ()
  (:panes
    (pane1 output-pane)
	(scroll-x scroll-bar)
	(scroll-y scroll-bar :orientation :vertical)
	(pane2 output-pane))
  (:layouts
    (top row-layout
	  '(pane1 scroll-y))
    (main-layout column-layout
	  '(top
	    scroll-x
		:divider pane2)))
  (:default-initargs
   :layout 'main
   :best-height 600
   :best-width 800))
   
When I resize using the divider, however, the horizontal scroll-bar 'flashes' (a
better description might be that it 'judders', seeming to slip out of place as I
move the divider). This doesn't occur if I just add scroll-bars
using the normal initargs, but I need to add them separately to implement my
scrolling. Any help on this very much appreciated.

Using Lispworks 5.1.1 Personal on XP.

Thanks in advance,
Chris