[plt-scheme] fluid-let and threads

Hi,

I am trying to understand the semantics of fluid-let in the presence  
of threads.

First, consider this program:

(define x 1)
(fluid-let ((x 2))
   (thread (lambda()
             (printf "~a~n" x)
             )))

prints a 1, which suggests that a thread created within a fluid-let  
does not see the fluid binding. Ok, that's a possibility.

But, it turns to be different if I add a bit of synchronization  
between the two threads. First, a variant that gives the same result  
(1):

(define x 1)
(define ch (make-channel))
(fluid-let ((x 2))
   (thread (lambda()
             (printf "~a~n" x)
             (channel-put ch 'ok))))
(channel-get ch)

Now, consider I move the channel-get within the fluid-let:

(define x 1)
(define ch (make-channel))
(fluid-let ((x 2))
   (thread (lambda()
             (printf "~a~n" x)
             (channel-put ch 'ok)))
   (channel-get ch)
)

I get 2!! meaning the value bound to x in the printf of the created  
thread is now 2. Just commenting out the "(channel-get ch)"  
expression, and I am back to getting a 1.

Any clarification is more than welcome!

Thank you,

-- Éric, completely puzzled

PS: using DrScheme 372 language MzScheme