[plt-scheme] sandbox.ss and user break

Hello,

Apparently sending a break to a thread which is running a sandboxed
evaluator doesn't work as expected. Is there a way to do this
properly?

/tmp/test.ss:

(require (lib "sandbox.ss"))

(define e
  (parameterize
      ((sandbox-output (current-output-port)))
    (make-evaluator '(begin) '())))
(e
 '(let again ()
    (display "x\n") (sleep 1) (again)))



Welcome to MzScheme v370 [3m], Copyright (c) 2004-2007 PLT Scheme Inc.
> (load "/tmp/test.ss")
x
x
  C-c C-cuser break

 === context ===
/usr/local/plt/collects/mzlib/sandbox.ss:440:4: evaluator

> x
x
x
x