External Drag and Drops are erratic in QQuickWidget due to QQuickDragAttachedPrivate::deliverMoveEvent relying on having a Window.

When using external drags in a QQuickWidget inside a ListViewDelegate, the drag target behaves erratically (i.e. on mouse release it'll attach to the cursor) and other weird behavior.

I believe this is due to QQuickDragAttachedPrivate::deliverMoveEvent/deliverLeaveEvent relying on having a window to send the leave event and hence the mousearea cannot cleanup afterwards.

i.e. The function reads:

void QQuickDragAttachedPrivate::deliverLeaveEvent()
{
    if (window) {
        QDragLeaveEvent event;
        deliverEvent(window, &event);
        window = 0;
    }
}

And when stepping through with a debugger, window == nullptr.

Update: See attached file for breaking case (comments for how to exhibit the behaviour)

Looking back on this, it's not so much external drags, it's more "automatic" drags which are used for external drags. Sorry for the incorrect language.