[racket] Syntax objects in prefab structures

The following program shows a difference between syntax objects stored
in prefab structures versus
transparent structures.

Is this a bug - or am I missing something about prefab structures?

#lang racket
(begin-for-syntax
  (struct foo (baz) #:prefab)
  (struct bar (baz) #:transparent)
  (define structs '()))

(define-syntax (macro1 stx)
  (set! structs (list (foo #'foox) (bar #'barx)))
  #'(void))

(begin-for-syntax (displayln (list 1 structs)))
(macro1)
(begin-for-syntax (displayln (list 2 structs)))

(define-syntax (with stx)
  (with-syntax ([s structs])
    #'(begin
        (begin-for-syntax
          (set! structs 's))
        (void))))

(with)

(begin-for-syntax (displayln (list 3 structs)))

The output is:

Welcome to DrRacket, version 6.1.1.4--2014-11-08(b7d2722d/d) [3m].
Language: racket; memory limit: 256 MB.
(1 ())
(2 (#s(foo .#<syntax:8:29 foox>) #(struct:bar .#<syntax:8:42 barx>)))
(3 (#s(foo foox) #(struct:bar .#<syntax:8:42 barx>)))
(1 ())
(2 ())
(3 (#s(foo foox) #(struct:bar .#<syntax:8:42 barx>)))
(1 ())
(2 ())
(3 (#s(foo foox) #(struct:bar .#<syntax:8:42 barx>)))

The syntax object in the prefab structure turned into a symbol !

--
Jens Axel Søgaard