Shared project content won't load in Phone project but will in Windows project

Content
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The Universal App template wasn’t available in the 3.2 build of MonoGame I was using (taken from the git repo just before Christmas) so I:

  • Created a MonoGame Windows project
  • Used the “make Windows Phone version” (paraphrased) action to create a second projetc in the solution for the phone
  • Created a separate solution with a MonoGame Windows Phone project, and spliced that over the top of the Phone project in the original solution
  • Moved the Game1.cs and all of the Content (raw PNGs) into the Shared project

I can build and run the Windows project fine, but the Windows Phone project crashes on start-up. If I add the relevantr MonoGame .csproj to my solution and use those, I can see that the asset loading can’t find the content assets on the phone version (the .xnb doesn’t exist). I don’t understand why loading the .pngs works on Windows but not on the Phone?

Shared classes work - should shared content work too?

[See also: Where is the MonoGame Content Builder GUI?]