[racket] formlet checkbox behaves differently from others

Here is my code:
#lang web-server/insta

(require web-server/formlets)

(define (start request)
  (define answer (get-answer "Formlet"))
  (response/xexpr
   `(html (head (title "formlet"))
          (body "Answer: " ,(format "~a" answer)))))

(define date-formlet
  (formlet
   (div "Month:" ,{input-int . => . month}
        "Day:"   ,{input-int . => . day})
   (list month day)))

(define travel-formlet
  (formlet
   (div "Name:" ,(input-string . => . name)
        (div "Depart:" ,{date-formlet . => . depart}
             "Return:" ,{date-formlet . => . return})
        (div "Car:" ,((select-input (list "No" "Avis" "Budget" "Hertz"))
                      . => . car))
        (div "Hotel:"  ,((checkbox "hotel" #f)
                         . => . hotel)))
   (list name depart return car hotel)))

(define my-formlet
  travel-formlet)

(define (get-answer label)
  (formlet-process my-formlet
                   (send/suspend
                    (λ (k-url)
                      (response/xexpr
                       `(html (head (title ,label))
                              (body
                               (form ([action ,k-url])
                                     ,@(formlet-display my-formlet)
                                     (input ([type "submit"])) ))))))))


I fill in the form and then I get the following:

Answer: (jon do (7 4) (7 21) Avis #(struct:binding:form input_6 hotel))

I sorta expected to see "hotel" here but I get the struct instead. Why is
this so?

Thanks in advance.
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