Description:
------------
Calling call_user_func(_array) more than one level deep will no longer take into account the callback object's state. E.g. 

call_user_func("call_user_func", $callback);

I am not entirely certain this is a bug: after all, usually once a function is called, an object's environment is left. However, call_user_func seems to be the exception to this rule, because the function would lose its significance otherwise.

Test script:
---------------
Anyway,

	class A {
		private function z() {
			echo __METHOD__;
		}
		
		public function x() {
			$callback = [[new $this(), "z"], []];
			$callback[0](...$callback[1]);
		}
	}
	
	(new A())->x();

	// This works fine and can be rewritten to:
	
	class A {
		private function z() {
			echo __METHOD__;
		}
		
		public function x() {
			$callback = [[new $this(), "z"], []];
			call_user_func_array("call_user_func_array", $callback);
		}
	}
	
	(new A())->x();

	Warning: call_user_func_array() expects parameter 1 to be a valid callback, cannot access private method A::z() in FILE.

Expected result:
----------------
Stacked invocation of call_user_func(_array) should not leave the callback object's state.

Actual result:
--------------
Stacked invocation of call_user_func(_array) leaves the callback object's state.