[plt-scheme] MrEd Designer broken in v350

The following code in MrEd designer raises an error in v350:

(define about-canvas%
  (class canvas%
    (define k-black (make-object color% 0 0 0))
; this raises the error: define: not allowed in an expression context.
    (define k-underline-brush (make-object brush% (make-object color% 0 0 
255) 'solid))
 .......


There was never a problem in previous versions, and I don't see anything 
relevant in the release notes; what is going on?

Thanks,

Nick Chubrich.