Index: src/core.js
===================================================================
--- src/core.js	(revision 3751)
+++ src/core.js	(working copy)
@@ -319,15 +319,15 @@
 	},
 
 	not: function( selector ) {
-		return this.pushStack(
-			selector.constructor == String &&
-			jQuery.multiFilter( selector, this, true ) ||
-
-			jQuery.grep(this, function(elem) {
-				return selector.constructor == Array || selector.jquery ?
-					jQuery.inArray( elem, selector ) < 0 :
-					elem != selector;
-			}) );
+		if (selector.constructor == String) 
+			return this.not(jQuery(selector));
+		else
+			return this.pushStack(
+				jQuery.grep(this, function(elem) {
+					return selector.constructor == Array || selector.jquery ?
+						jQuery.inArray( elem, selector ) < 0 :
+						elem != selector;
+				}) );
 	},
 
 	add: function( selector ) {
Index: src/selector.js
===================================================================
--- src/selector.js	(revision 3751)
+++ src/selector.js	(working copy)
@@ -320,7 +320,7 @@
 			// :not() is a special case that can be optimized by
 			// keeping it out of the expression list
 			if ( m[1] == ":" && m[2] == "not" )
-				r = jQuery.filter(m[3], r, true).r;
+				r = jQuery(r).not(m[3]).get();
 
 			// We can get a big speed boost by filtering by class here
 			else if ( m[1] == "." )