[plt-scheme] Bug in Syntax Certification?

Hello,

I'm seeing a weird error message when I try to use iteration macros  
outside the module I defined them in.  For example, the following  
breaks (in the scheme language in DrScheme, version 4.0.0.1- 
svn13jun2008):

(require (planet wmfarr/simple-matrix:1/matrix))
(for/list ((x (in-matrix (matrix* 2 2 1 2 3 4)))) x)

with the error

compile: access from an uncertified context to unexported variable  
from module: "/Users/farr/Documents/code/simple-matrix/matrix.ss" in:  
matrix-elts

There are two weird things about this error:

1. matrix-elts is exported from the matrix.ss module.
2. I haven't been playing with certifying identifiers at all (in fact,  
I have only a vague notion of what certifying an identifier means).

Is this because I've used define-sequence-syntax to define in-matrix  
inappropriately (the code for in-matrix and its companion procedure  
*in-matrix is given below)?  Is this a problem with the syntax  
expander in Friday's SVN?  Should I just file this as a bug in the bug  
reporter, or is it a quick fix?

Sorry for the trouble, and thanks for any help you all can give me!

Will

-----------------------
Code for in-matrix:

(define (*in-matrix m)
   (make-do-sequence
    (lambda ()
      (values
       (lambda (k)
         (vector-ref (matrix-elts m) k))
       add1
       0
       (lambda (k) (< k (* (matrix-rows m) (matrix-cols m))))
       (lambda (elt) #t)
       (lambda (k elt) #t)))))

(define-sequence-syntax in-matrix
   (lambda () (syntax *in-matrix))
   (lambda (stx)
     (syntax-case stx ()
       (((id) (_ matrix-expr))
        (syntax/loc stx
          ((id) (in-vector (matrix-elts matrix-expr)))))
       (((i-id j-id elt-id) (_ matrix-expr))
        (syntax/loc stx
          ((i-id j-id elt-id)
           (:do-in
            (((m) matrix-expr)) ;Outer bindings.
            #t ; Outer check
            ((i-id 0) (j-id 0) (rows (matrix-rows m)) (cols (matrix- 
cols m))) ;Loop id
            (< i-id rows) ; Pos-guard
            (((ip1) (add1 i-id)) ((jp1) (add1 j-id)) ((elt-id) (matrix- 
ref m i-id j-id))) ; Inner-id.
            #t ; Pre-guard
            #t ; Post-guard
            ((if (>= jp1 cols) ip1 i-id) (if (>= jp1 cols) 0 jp1) rows  
cols))))))))