Usually when I plug my macbok into an external monitor both displays show the same thing. However when I just plugged my macbook into the display whilst it was on sleep then woke it up the external display came on but nothing would wake the screen on the macbook. Even when I went into the displays option it did not have the usual "arrangement" tab. It only started working again when I restarted the macbook. Is this usual behaviour or is it acting weird?