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 ) {