image-access memory leak

I need to analyze several thousands of png images (frames of a film). I read pixels via image-access. Here is a test function filling a vector with pixels of one image. The vector is created if not supplied, *test-pane* is a capi:output-pane.

(defun test-load-image (path &optional vector)
  (let* ((im (gp:load-image *test-pane* 
                            (gp:read-external-image path)
                            :editable t))
         (vec (if vector
                  vector
                (make-array (* (gp:image-height im) (gp:image-width im) 4) 
                            :element-type '(unsigned-byte 8))))
         (acc (gp:make-image-access *test-pane* im)))
    (gp:image-access-transfer-from-image acc)
    (gp:image-access-pixels-to-bgra acc vec)
    (gp:free-image-access acc)
    (gp:free-image *test-pane* im)
    vec))

Images are 1920 × 1080 pixels, about 1.4 MB each. I experience a huge memory leak (Gigabytes) when using this function about 1000 times. Any ideas? I use LWM 8.1.

Thanks,

Michal

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