The custom fields set in search/jobs POST are not returned in search/jobs GET. In earlier versions of splunk the custom fields were returned. However they are missing in 7.0.7
As per documentation http://docs.splunk.com/Documentation/Splunk/7.0.7/RESTREF/RESTsearch#search.2Fjobs , the custom fields should be available in GET.
Is this a bug?
Note: in Splunk 7.0.7, the custom fields are returned only for search/jobs/<search-id> end point.
Splunk has accepted that it is a bug and they will fix it.