Product Version = NetBeans IDE Dev (Build 201011190001)
Operating System = Linux version 2.6.35-22-generic running on amd64
Java; VM; Vendor = 1.6.0_22
Runtime = Java HotSpot(TM) 64-Bit Server VM 17.1-b03

Having experimental hints turned on (that's why P4) hint that variable might have not been initialized is shown for variable in a declaration of a function (see attached image).

Expected: No warning shown. 

To reproduce copy/paste to PHP file:
// {{{ constants

/**
 * Holds the path to the source files
 */
define('BASE_PATH',
        dirname(__FILE__) . \DIRECTORY_SEPARATOR . '..'
        . \DIRECTORY_SEPARATOR . '..' . \DIRECTORY_SEPARATOR);
// }}}

/**
 * Define and register autoloader function
 */
if (false === \spl_autoload_register(function ($className) {
                    require \BASE_PATH . str_replace(
                                    "\\", \DIRECTORY_SEPARATOR, $className
                            ) . ".php";
                })) :
    throw new Exception("Unable to register autoload function.", 248);
endif;