Problem

If you compile git-plugin from the source, and set 'Discard old items' in the multibranch pipeline, deleted branches on the SCM are not deleted from the job list. If you install the 2.5.3 version of this plugin and restart Jenkins, these branches are deleted.

How to reproduce it

Configure a Jenkins installation

1. Download a fresh Jenkins (2.7.2), rename your current home
2. Start it: java -jar jenkins.war
3. Choose the default packages option during the first boot
4. Clone git-plugin repository, compile it (mvn.cmd '-Dmaven.test.skip=true' clean install hpi:hpi)
5. Import your git-plugin (the one you compiled) in Jenkins (advanced tab)
6. Restart Jenkins

See the error

1. Create a test git repository with a Jenkinsfile on many branches
2. Add a new multibranch pipeline, select "Discard old items"
3. Save, check that your branches appear in the list
4. Delete a branch from your repository. git push origin :features/a-random-branch
5. Run a branch indexing
6. See that your branch was not deleted

Check that 2.5.3 is working

1. Restore the git-plugin in its original version, 2.5.3
2. Restart Jenkins
3. Rerun branch indexing, see that your branch has disappeared !

Investigations

I didn't have the time to run a Jenkins instance in debug, or to read the commits yet. So I've no idea why this bug happens. I'll update this section later if I've time.