[racket] Problem with scribble examples written in linked language

I am trying to scribble some examples using a custom evaluator.  if I 
use the example from the documentation, things work:

@(require racket/sandbox
           scribble/eval)
@(define my-evaluator
    (parameterize ([sandbox-output 'string]
                   [sandbox-error-output 'string])
      (make-evaluator 'typed/racket/base)))
@interaction[#:eval my-evaluator

              (: my-sqr (Real -> Real))
              (define (my-sqr x)
                (* x x))
              (my-sqr 42)]

But when I change the language from 'typed/racket/base to 'pcf/lang (a 
collection that I've added with raco link).  Then I get a sandbox error:

file-exists?: `exists' access denied for 
/Users/dvanhorn/Documents/git/racket/bin/racket
   context...:
    find-executable-path
 
/Users/dvanhorn/Documents/git/racket/collects/setup/private/main-collects.rkt:19:4: 
find-main-collects
 
/Users/dvanhorn/Documents/git/racket/collects/racket/private/promise.rkt:104:10
 
/Users/dvanhorn/Documents/git/racket/collects/racket/private/more-scheme.rkt:263:2: 
call-with-exception-handler
    /Users/dvanhorn/Documents/git/racket/collects/racket/private
...

Am I doing something wrong, or is this a buggy interaction between the 
sandbox and raco link?

Thanks,
David