When asked why they put quotation marks around a character’s name and why they thought “details are mum” made sense, the editors at yahoo.com are mum:
If the name of the movie Mr. Affleck will direct is “Batman,” then it deserves quotation marks. But it’s not. That’s the name of the character that will be central to a movie. Character names don’t get special treatment. You wouldn’t write about “Romeo” and “Juliet” would you? (Well, if you’re a Yahoo! editor you might, but the rest of the English-speaking world wouldn’t.) And why tell us that “details are mum”? Because aren’t details always silent? Perhaps it was the producer who is mum and details are missing or nonexistent.