Ticket #2811: add.diff

core.js

@@ -339 +339 @@
         },
 
         add: function( selector ) {
-                return !selector ? this : this.pushStack( jQuery.merge( 
+                return this.pushStack( jQuery.unique( jQuery.merge( 
                         this.get(),
-                        selector.constructor == String ? 
-                                jQuery( selector ).get() :
-                                selector.length != undefined && (!selector.nodeName || jQuery.nodeName(selector, "form")) ?
-                                        selector : [selector] ) );
+                        typeof selector == 'string' ? 
+                                jQuery( selector ) :
+                                jQuery.makeArray( selector )
+                )));
         },
 
         is: function( selector ) {