In T82002#1133093, @Anton Raves (Memento) wrote:

When there is a default button, that entire dialog / window should respond to pressing the "Enter" or "Return" key, not just when the mouse is in / hovering over a smaller area of that dialog / window.

There should be no obvious default button when the application only listens to a (mouse inside) smaller area or when that dialog / window is not the front dialog / window!

Its consistent when you place your mouse cursor just above where you'd type in the file name (in the grey area between the file name and browser window).