list-box% label width in Windows/OS X

The label width in a list-box% never changes from its default in Windows and OS X. Consider the following code:

#lang racket/base
(require racket/class
         racket/gui/base)

(define frame
  (new frame%
       [label "foo"]
       [width 300]
       [height 400]))

(define lbox
  (new list-box%
       [parent frame]
       [label "123"]
       [choices '("a" "b" "c")]
       [style '(single vertical-label)]
       [callback (λ (lb evt)
                 (send lb set-label "123456"))]))

(send frame show #t)

On Gentoo, the label changes properly from "123" to "123456", yet on Windows and OS X the label appears unchanged, but what is actually happening is the label is changed and the width of the label is unchanged.

Start by running the supplied racket/gui/base example on Windows and OS X, then compare the label behavior with Gentoo. Trace the list-box% vertical-label update path and platform-specific width handling; done means changing the label also updates its visible width on the affected platforms.