I just noticed this today when creating a new quiz. When building the quiz, I selected a MC question, and it presented me with 4 blank answers. I filled in text for two of the choices, leaving the other two blank.
When I saved and previewed the quiz, that question showed me four answers, with two of them having blank answers. I don't recall seeing blank answers turn into active answers in the past, but I honestly wasn't paying that close attention. Is this expected behavior, is this a bug?