ignoring free identifiers list in sintactic closures

The following code is expected to output (12 2), and it does so in both MIT and Chibi schemes. But it Unsyntax 0.0.3.23-b7aa it outputs (2 2).

(import (scheme base)
        (scheme cxr)
        (scheme write)
        (srfi 211 syntactic-closures))

(define-syntax macro
  (sc-macro-transformer
   (lambda (form env)
     (let ((p1 (make-syntactic-closure env '() (cadr form)))
           (p2 (make-syntactic-closure env '(internal) (caddr form))))
       `(let ((internal 1))
          (list ,p1 ,p2))))))

(let ((internal 11))
  (display (macro (+ internal 1) (+ internal 1))))
(newline)