After ripping completes there is a popup window.
If you swap the media while this popup is open, MakeMKV does not detect the media swap.
After clicking ok, you are back at the title selection page of the old media.
You have to either eject the media again and reinsert it, or restart MakeMKV.
MakeMKV should notice the media change event, and automatically go back to the start page.
P.