Section Split Segment disabled - RVT 2014

[JohnnyFortune]

Attached is a project file that I have trimmed down to nearly nothing attempting to troubleshoot why split segment is disabled for a section cut. In plan view see section that for whatever reason I cannot split segment as the button is disabled. I've never seen this and am trying to determine what caused it. I think this project was started in Revit 2014 (no upgrade). Obviously I can create new sections and split them but on a full project when this happens it is a real pain as sections often contain many embellishments. So basically, I don't need a workaround -- just trying to determine what causes this so we can avoid in the future.

Any ideas?

Thanks ahead of time for any help you can give.