Please stop putting action/choice buttons (Ok, Cancel, Yes, No, etc.) on windows title bars! There has been a reason why they were placed at the bottom: I grab a window by its title bar and if needed I can arrange it through the closest controls over there that should be only the buttons to act on the window itself and not the contents, then I read the contents and while doing so my focus moves towards the window lower side, so that when I'm done I can take a choice through the closest controls I can find there which are the ones acting on the content of the window.

You think title bars waste too much space? Well sometimes I do too, but placing controls on them is a solution that creates new problems; just make them thinner, but please stop breaking decades of functional UI design with this nonsense.