macro stepper derivation error with repeated define-syntax

[rfindler]

This program:

#lang racket/base
(require (for-syntax racket/base))
(define-syntax x 1)
(define-syntax x 2)

when given to the macro stepper produces a window with the message "Macro stepper error (derivation) [details]."

The details produces this error:

Internal error:
derivation-parser: error on token #270: <ERROR, #(struct:exn:fail:syntax "module: identifier already defined" #<continuation-mark-set> (#<syntax:6-unsaved-editor:4:15 x>))>