Index: t3lib/class.t3lib_div.php
===================================================================
--- t3lib/class.t3lib_div.php	(revision 5022)
+++ t3lib/class.t3lib_div.php	(working copy)
@@ -4682,13 +4682,22 @@
 		}
 
 			// Get final classname
-		$className =  t3lib_div::makeInstanceClassName($className);
+		$className = self::getClassName($className);
 
 		if (isset($instances[$className])) {
 				// it's a singleton, get the existing instance
 			$instance = $instances[$className];
 		} else {
-			$instance = new $className;
+			if (func_num_args() > 1) {
+					// removing the method's first argument (the class name)
+				$constructorArguments = func_get_args();
+				array_shift($constructorArguments);
+
+				$reflectionObject = new ReflectionClass($className);
+				$instance = $reflectionObject->newInstanceArgs($constructorArguments);
+			} else {
+				$instance = new $className;
+			}
 
 			if ($instance instanceof t3lib_Singleton) {
 					// it's a singleton, save the instance for later reuse
@@ -4712,6 +4721,17 @@
 	}
 
 	/**
+	 * Return classname for new instance, takes the class-extensions API
+	 * of TYPO3 into account.
+	 *
+	 * @param	string		Base Class name to evaluate
+	 * @return	string		Final class name to instantiate with "new [classname]"
+	 */
+	protected function getClassName($className) {
+		return class_exists('ux_'.$className) ? self::getClassName('ux_'.$className) : $className;
+	}
+
+	/**
 	 * Find the best service and check if it works.
 	 * Returns object of the service class.
 	 *
Index: typo3/backend.php
===================================================================
--- typo3/backend.php	(revision 5022)
+++ typo3/backend.php	(working copy)
@@ -140,9 +140,7 @@
 		);
 
 		foreach($coreToolbarItems as $toolbarItemName => $toolbarItemClassName) {
-				// Get name of XCLASS (if any):
-			$toolbarItemClassName = t3lib_div::makeInstanceClassName($toolbarItemClassName);
-			$toolbarItem = new $toolbarItemClassName($this);
+			$toolbarItem = t3lib_div::makeInstance($toolbarItemClassName, $this);
 
 			if(!($toolbarItem instanceof backend_toolbarItem)) {
 				throw new UnexpectedValueException('$toolbarItem "'.$toolbarItemName.'" must implement interface backend_toolbarItem', 1195126772);