Threads trouble

Hello,

consider this program:

   ;; ,open threads

   (define-syntax run/strings-status
     (syntax-rules ()
       ((_ epf ...)
        (call-with-values
            (lambda ()
              (run/port+proc epf ...))
          (lambda (port proc)
            (let* ((string-list (port->string-list port))
                   (status (wait proc)))
              (close-input-port port)
              (values string-list status)))))))

   (define my-ls
     (lambda ()
       (receive (out rc)
           (run/strings-status (ls))
         out)))

Now try:

   > (my-ls)
   '("COPYING" "INSTALL" "Makefile" ...)

   > (spawn (lambda () (run (ls))))
   > COPYING   Makefile.in  build  config.guess   config.sub    doc	    go		 scheme       scsh-config.in
   INSTALL   README       c      config.log     configure	   emacs    install-sh	 scsh	      scsh.image
   Makefile  RELEASE      cig    config.status  configure.in  gdbinit  ps-compiler  scsh-config  scshvm

So far, so good.  But now try this:

   > (spawn my-ls)
   > 

As you see, there is no output from `ls', as I expected.  This happens
with 0.6.6 as well as with 0.6.7-rc1.

Is this a bug or am I overseeing something obvious?

Thanks for your time.

-- 
Emílio C. Lopes
Munich, Germany