To be able to do some research on ghprb, I've cloned https://github.com/jenkinsci/ghprb-plugin.git, checked out ghprb-1.32.4, and built it with mvn clean package. Tests go through w/o any problem (Tests run: 53, Failures: 0, Errors: 0, Skipped: 0).

Now the odd thing: With the original version installed via jenkins update center (which is 1.32.4 as well), webhook delivery via GitHub work. But as soon as I "scp ${BUILD_DIR}/target/ghprb.jar ${JENKINS_HOST}:${JENKINS_HOME}/plugins/ghprb/WEB-INF/lib/ghprb.jar" and restart jenkins on this host, webhook delivery fails with

Jun 13, 2016 8:10:55 AM hudson.security.csrf.CrumbFilter doFilter
WARNING: No valid crumb was included in request for /ghprbhook/. Returning 403.

As soon as I copy back the original jar file and restart jenkins, webhook delivery works again (veryfied by clicking the Redliver button on GitHub).

So I wonder, what's going wrong here.