[racket] Confusing behavior with continuation-marks

I was looking at the documentation on how continuation-marks work, and
the documented behavior is different than what I observed.

The following programs add a continuation mark, then a prompt, then
try to look at the current continuation marks. According to the
documentation I would expect the programs not to find a continuation
mark, but in some cases it does. Here are the 6 variations and their
returned values.


#lang racket
(define key 'key)
(define value 'value)
(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      #f
      key))))

(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      (current-continuation-marks)
      key))))

(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      (current-continuation-marks (default-continuation-prompt-tag))
      key))))

(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      #f
      key
      (default-continuation-prompt-tag)))))

(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      (current-continuation-marks)
      key
      (default-continuation-prompt-tag)))))

(with-continuation-mark key value
  (call-with-continuation-prompt
   (lambda ()
     (continuation-mark-set-first
      (current-continuation-marks (default-continuation-prompt-tag))
      key
      (default-continuation-prompt-tag)))))

=>
'value
#f
#f
'value
#<continuation-prompt-tag:default>
#<continuation-prompt-tag:default>


-Eric