I'm halfway there - got single tracks to drag and drop by changing Cubase Import Settings to "use settings" so that there's no dialogue box when dragging.

But the drag master/all tracks still causes Cubase to hang, when the dialogue box asks if they should be on one track or different tracks. There doesn't seem to be a way around that dialogue box, so master track drag 'n drop causes a freeze every time.

Has anyone else encountered this?