[racket] drracket 5.0.2 does not start on Freebsd 8-stable

the error msg is 
set-box!: expects argument of type <mutable box>; given
1220200079198261331

 === context ===
/usr/local/lib/racket/collects/framework/main.rkt: [running body]
/usr/local/lib/racket/collects/drracket/tool-lib.rkt: [traversing
imports]
/usr/local/lib/racket/collects/drracket/private/drracket-normal.rkt:
[running body]
/usr/local/lib/racket/collects/drracket/drracket.rkt: [running body]


Since this seems to be an active port and I found nothing about this
error, I assume it should work...

How can I go on debugging this error?

Thanks, Mathias

P.S.: it's running in xorg 7.5, gnome (with xmonad or metacity)