Relative namespaces and call_user_func()

Code speaks better than words:

namespaces.php:

<?php

namespace foo;

use foo\models;

class factory
{
    public static function create($name)
    {
        /*
         * Note 1: FQN works!
         * return call_user_func("\\foo\\models\\$name::getInstance");
         *
         * Note 2: direct instantiation of relative namespaces works!
         * return models\test::getInstance();
         */

        // Dynamic instantiation of relative namespaces fails: class 'models\test' not found
        return call_user_func("models\\$name::getInstance");
    }
}

namespace foo\models;

class test
{
    public static $instance;

    public static function getInstance()
    {
        if (!self::$instance) {
            self::$instance = new self;
        }

        return self::$instance;
    }

    public function __construct()
    {
        var_dump($this);
    }
}

namespace_test.php:

<?php

require_once 'namespaces.php';

foo\factory::create('test');

As commented, if I use the full-qualified name inside call_user_func() it works as expected, but if I use relative namespaces it says the class was not found – but direct instantiations works. Am I missing something or its weird by design?