Fix for http://dev.jquery.com/ticket/6451

src/ajax.js

@@ -237,16 +237,23 @@ jQuery.extend({
 			s.dataType = "script";
 
 			// Handle JSONP-style loading
-			window[ jsonp ] = window[ jsonp ] || function( tmp ) {
+			var customJsonp = window[ jsonp ];
+			window[ jsonp ] = function( tmp ) {
 				data = tmp;
 				jQuery.ajax.handleSuccess( s, xhr, status, data );
 				jQuery.ajax.handleComplete( s, xhr, status, data );
+				
+				if ( jQuery.isFunction( customJsonp ) ) {
+				    customJsonp( tmp );
+			    }
+			    else {
     				// Garbage collect
     				window[ jsonp ] = undefined;
 
     				try {
     					delete window[ jsonp ];
     				} catch( jsonpError ) {}
+                }
                 
 				if ( head ) {
 					head.removeChild( script );
@@ -436,8 +443,9 @@ jQuery.extend({
 				}
 
 				// Fire the complete handlers
+				if ( !jsonp ) {
 				    jQuery.ajax.handleComplete( s, xhr, status, data );
-
+                }
 				if ( isTimeout === "timeout" ) {
 					xhr.abort();
 				}

test/unit/ajax.js

@@ -1225,6 +1225,12 @@ test("jQuery.ajax - Etag support", function() {
 	});
 });
 
+
+test("jQuery.ajax - active counter", function() {
+    ok( jQuery.ajax.active == 0, "ajax active counter should be zero: " + jQuery.ajax.active );
+});
+
+
 }
 
 //}