Photo courtesy of David Backlin (taken February 2007)
The angled-arrow symbol normally is used to indicate that your current route will be turning at an upcoming intersection. In Nixa, it appears that, instead, the arrow is used to indicate a turn at this intersection. That's not correct, because US 160 and Missouri 13 are concurrent through Nixa. So it counts as a goof, though it's more subtle than the typical goof.
The routing for Missouri 13 is shown correctly.