I used LDAP authentication for a while, then changed to a different authentication plugin. Because I was no longer using LDAP, I decided to uninstall the LDAP plugin, which was at, I think, version 1.20 at the time. The Uninstall button was available in the plugin manager. After using it and restarting Jenkins, it turned out that the plugin was not actually uninstalled, it had just reverted to 1.11. In fact even deleting the files from /var/lib/jenkins/plugins and restarting Jenkins didn’t uninstall the plugin; it reappeared after a restart.

Investigation revealed that the LDAP plugin is apparently bundled with Jenkins. IMO one of the following should be true:

• The uninstall button for bundled plugins should actually uninstall the plugin and make it stay uninstalled, or
• The uninstall button should not be present for bundled plugins, or
• The uninstall button should be replaced with a “downgrade to bundled version” button, making it clear that it would not actually uninstall anything.