Description:
------------
When calling non-static method from object method, that method has wrong $this, pointing to object from which call does (example one). Also it is security problem - attacker may "override" (not real overriding) private method (example two).

Test script:
---------------
Example one:
class A {
    function aaa() {
        echo get_class($this);
    }
}

class B {
    function bbb() {
        A::aaa();
    }
}

(new B())->bbb();


Example two:
class PasswordManager {
    private function getPasswordHash($rawPassword) {
        return md5($rawPassword);
    }
    private function isPasswordValid($rawPassword, $hashPassword) {
        return $hashPassword === $this->getPasswordHash($rawPassword);
    }
    public function authorize($rawPassword, $hashPassword) {
        if ($this->isPasswordValid($rawPassword, $hashPassword)) {
            echo "Congratulations! You are authorized!\n";
            return true;
        }

        echo "Sorry! Authorization failed!\n";
        return false;
    }
}

class Attacker {
    public function isPasswordValid($a, $b) {
        return true;
    }
    public function doAttack() {
        PasswordManager::authorize(null, null);
    }
}

(new Attacker())->doAttack();



Expected result:
----------------
Example 1:
NULL

Actual result:
--------------
Example 1:
B