[racket] Step function in HTDP intermediate student

Hi, I have a question regarding the step function in DrRacket under
the HTDP intermediate student language. It seems that whenever there
is a local "define-struct" the step function would fail.  Consider a
program:

;;;;;;;;;;;;;;;;;;;;;;;;;;
(define (f x)
  (local ((define-struct a (b c)))
    x))

(f 1)
;;;;;;;;;;;;;;;;;;;;;;;;;;

Choose the HTDP intermediate student language, click run, then click
the step button, DrRacket would produce the following message in the
step window:

;;;;;;;;;;;;;;;;;;;;;;;;;;
annotate-inner: nothing expands into begin! : (list 'begin (list
'#%app 'raw 'r) (list '#%app 'check-struct-wraps! 'r) (list '#%app
'raw 'r))
;;;;;;;;;;;;;;;;;;;;;;;;;;

I am using Racket version 5.0.1 (the Ubuntu jaunty i386 download).

Thanks,
--Yang