Sprite texture incorrect

Unity 5, I modified the default sprite shader to include a mask image. Everything works fine in the editor, but then when I click play, for some reason the texture passed as the sprite texture is broken...

The left image is before hitting play, the right image just after hitting play. The texture passed as Sprite Texture to the shader, for some reason, is incorrect. You can see the exact same sprite is used.

There are no scripts at all in the scene.

Ideas? Bug?