[racket] struct-copy and custom-write bug?

When I put the following in the DrRacket definitions window and then 
evaluate t, it works for a few seconds and runs out of memory. Anyone 
understand the problem?

#lang racket

(define (Print stx port mode)
   (if (Atom? stx)
       (write-string "ATOM " port)
       (Print (Pair-cdr stx) port mode)))

(struct Base ()
   #:methods gen:custom-write
   [(define write-proc Print)])

(struct Atom Base (datum))
(struct Pair Base (car cdr))

(define t (struct-copy Base (Atom  3)))