I guess I would add the fix to
(defun org-babel-execute:rec (body params) etc)
but where?
Apply this patch to your local copy:
diff --git a/etc/ob-rec.el b/etc/ob-rec.el
index 2c3de44..38996aa 100644
--- a/etc/ob-rec.el
+++ b/etc/ob-rec.el
@@ -38,6 +38,7 @@ This function is called by `org-babel-execute-src-block'."
(error
"rec code block requires :data header argument")))
(cdr (assoc :data params))))
+ (result-params (cdr (assq :result-params params)))
(cmdline (cdr (assoc :cmdline params)))
(rec-type (cdr (assoc :type params)))
(fields (cdr (assoc :fields params)))