[plt-scheme] mred -z weirdness

When I put these lines from the MrEd manual into a file:

  ;; Make a frame by instantiating the frame% class
  (define frame (instantiate frame% ("Example")))

  ;; Make a static text message in the frame
  (define msg (instantiate message% ("No events so far..." frame)))

  ;; Make a button in the frame (using keyword-based arguments, for demonstration)
  (instantiate button% () (label "Click Me") (parent frame)
	       ;; Callback procedure for a button click
	       (callback (lambda (button event) (send msg set-label "Button click"))))

  ;; Show the frame by calling its show method
  (send frame show #t)

and run "mred" and load it with the "File->Load file" menu item, it
works fine.  (It works fine with "drscheme" also.)  However, when I
run "mred -z" and use the "load" function, I get a blank (empty)
window.  This happens in both Linux/X and Windows.  I'm using version
200alpha19.  Is this a bug?  Is -z (which runs the repl via stdio
instead of a window) not fully supported?

--dougo at ccs.neu.edu