Comment 43 for bug 38753

But Windows is able to slightly improve the usability by knowing *before* mouse-up whether a click *can* be a drag. If it can't (i.e. you clicked something non-draggable) then it raises the window immediately.

This requires a reply to all mouse-down events from the window saying "This might be a drag, don't raise me immediately" or "There's no chance this is a drag, raise me now." I had a look at the Wayland protocol, and it doesn't seem to include anything like this.

Of course you could simply always wait for mouse-up, but then it will seem less responsive.