The issue was in the fact that the selected Field Template was “Default”, when it should be “Only content”. That’s why it was adding extra fields in the html and as a result it wasn’t rendering correctly.
Thanks for reporting it, I will also add it in the webtools along with a How-to. I also modified the post title in order to be easier tracable.
This answer solved a similar problem I had with “Teaser List”. I agree with you, it would be good idea to write it down in the respective documentation, because it’s not so obvious.
My prosed extension in the current documentation:
… After choosing the layout, go to pattern settings and in Field templates select “Only content” and then click on “Save configuration”.