Index: wp-includes/js/wp-lists.dev.js
===================================================================
--- wp-includes/js/wp-lists.dev.js	(revision 17949)
+++ wp-includes/js/wp-lists.dev.js	(working copy)
@@ -346,7 +346,7 @@
 
 		} else if ( s.pos < 0 ) {
 			list.prepend(e);
-		} else {
+		} else if ( 0 === $('#' + s.element).size() ) {
 			list.append(e);
 		}