Don't attempt to remove result when :results silent.

lisp/org-babel.el

@@ -448,7 +448,8 @@ silent -- no results are inserted"
         (setq result (org-babel-clean-text-properties result))
         (if (member "file" insert) (setq result (org-babel-result-to-file result))))
     (unless (listp result) (setq result (format "%S" result))))
-  (if (and insert (member "replace" insert)) (org-babel-remove-result))
+  (if (and insert (member "replace" insert) (not (member "silent" insert)))
+      (org-babel-remove-result))
   (if (= (length result) 0)
       (if (member "value" result-params)
 	  (message "No result returned by source block")