[plt-scheme] SGL - swap-buffers

This does not work on RedHat Linux (DrScheme loops and then crashes):

...
(define (on-paint)
  (send this with-gl-context (lambda () (draw)))
  (send this swap-gl-buffers))
...

However, this does

...
(define (on-paint)
  (send this with-gl-context
         (lambda ()
           (draw)
           (send this swap-gl-buffers))))
...

Same with swap-buffers.

Is it intended that swap-gl-buffers and swap-buffers work only inside
with-gl-context or am I doing something wrong?

Regards,

Zbyszek Jurkiewicz