Hi Geoff,
I tried everything from your lists. The problem is still there.
Adding the code you suggested gives me back 500 error. I decided not to investigate why.
I reproduce all the step from the other link and switched to the twenty-fourteen theme. Got the same broken links.
If you edit organiser or venue you can see the link to the object is already broken. When you switch back to English the link looks like it should and works properly.
http://yoga22mayak.com/wp-content/uploads/2016/01/Screen-Shot-2016-01-05-at-18.46.57-1024×212.jpg