FYI There was a comment made in Atlassian jira about this:
We are no longer actively developing JIRA's XML-RPC or SOAP APIs. We recommend using our REST APIs instead. Please see https://developer.atlassian.com/display/JIRADEV/_JIRA+API+Status for the current status of our various APIs.
The api status link says they wont be fixing any bugs in anything but REST api:
Deprecated in JIRA 6.0. This means that we will not add new features nor fix bugs related to the XML-RPC API during the JIRA 6.x lifecycle. Read the deprecation announcement for more information.
...so they closed the bug ticket. Seems like this jenkins jira plugin ticket needs to be converted to a migrate to supported REST API?