[racket] call/comp, eq? and call-with-continuation-prompt

For some reason the below program returns false:

#lang racket
(define g #f)
(define p (make-continuation-prompt-tag))
(define (t)
  (let ([a (cons 1 2)])
    (call-with-composable-continuation (λ (k) (set! g k)) p)
    a))
(call-with-continuation-prompt t p)
(eq? (call-with-continuation-prompt g p)
       (call-with-continuation-prompt g p))

This happens with call/cc as well. From my understanding a should be
allocated before the continuation is captured, so the two calls to g should
return the same cell. If I remove the prompt tag the program returns true.

Anyone have any clue whats going on or how to fix?

--Spencer
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