why is an underscore displaying in element name?

[awootton1]

In the diagnostic report resource, when the IssuedElement is null...and the IssuedElement.Extension is set to the data absent reason string, I am seeing an underscore in the element name when I do my POSTMAN POST.

[mbaltus]

This is how FHIR has specified to put an extension on a primitive data element in JSON. See http://hl7.org/fhir/json.html#primitive for more information.