Strange behavior in PHP

test.php

<?php

class C1 {
    protected $propertyProtected = 'foo';
}

class C2 {
    public function test() {
        $objC1 = new C1();
        echo $objC1->propertyProtected;
    }
}

class C3 extends C2 {
    public function test() {
        $objC1 = new C1();
        echo $objC1->propertyProtected;
    }
}

class C4 extends C1 {
    public function test() {
        $objC1 = new C1();
        echo $objC1->propertyProtected;
    }
}

// Fatal error: Cannot access protected property
//$objC1 = new C1();
//var_dump($objC1->propertyProtected);

// Fatal error: Cannot access protected property
// $objC2 = new C2();
// $objC2->test();

// Fatal error: Cannot access protected property
//$objC3 = new C3();
//$objC3->test();

// Why it works? Inside test() method I'm accessing a property in another object, 
// not in a parent object. It isn't $this->propertyProtected;
// $objC4 = new C4();
// $objC4->test();