Suddenly in some application Ubuntu stopped showing the menu bar (having buttons for maximize, minimize, close) and also it only starts them on the top left corner, and without the menu bar moving them is not easy.
However, this is specific to some applications. For example, Firefox and Netbeans have the menu bar but Nautilus and Terminal do not have it.
I'm using Ubuntu 16.04 and I just updated it. Maybe the problem is relevant to the update.