PHP static function being called in dynamic environment

Since when PHP allows to call static function like a dynamic function?

I am using php 5.3.2

class weird{

    public static function iamstatic($calledFrom){
            echo "I am  a static function called with  a $calledFrom operator\n";
    }

    public function test(){
            self::iamstatic("static");
            $this->iamstatic("dynamic");
    }

 }

$c = new weird();
$c->test();

weird::iamstatic("Static outside class");
$c->iamstatic("Dynamic outside class");

This outputs :

I am  a static function called with  a static operator
I am  a static function called with  a dynamic operator
I am  a static function called with  a Static outside class operator
I am  a static function called with  a Dynamic outside class operator