While working on an extension filter plugin for GitHub PR labels which adds an SCMHeadEvent implementation I noticed that the constructors for PullRequestSCMHead and PullRequestSCMRevision were package private. Using more generic classes, the scm source rejects the heads returned by the event and so the subscriber cannot operate. A locally modified version of GHBS with public constructors allowed the new plugin to work correctly.

Discussion at https://groups.google.com/forum/#!topic/jenkinsci-dev/bLoYi3munDw