I see spurious double clicks appearing in a QML MouseArea during a drag operation starting in that MouseArea and leaving the window, while crossing the OSX window titlebar. Though I have not yet managed to isolate a repro, I have managed debug sufficiently to understand the problem:

If frameStrutEventsEnabled() is set for the QCocoaWindow(), handleFrameStrutMouseEvent is called with NSLeftMouseDragged events.

In qnsview.mm, the handleFrameStrutMouseEvent routine has a switch statement that handles NSLeftMouseDown and NSLeftMouseUp but ignores NSLeftMouseDragged, so it creates a FrameStrutMouse event with no buttons pressed (even though the Dragged event indicates that I am still holding a button!)

QGuiApplicationPrivate::processMouseEvent then processes this event and interprets it as QEvent::NonClientAreaMouseButtonRelease storing the wrong information about the non-pressed buttons and causing a subsequent mouse move (with buttons still pressed) to simulate a double-click.