With Job Import plugin installed (and not configured, if it matters), when you go to Manage Jenkins -> Configure System and then click "Save," you are redirected back to the configuration edit page, rather than back to the Manage Jenkins page. It's as though you clicked the "Apply" button instead of "Save." I don't see anything jumping out at me when I look at the js console when this happens, but I have confirmed Job Import plugin is the culprit. Uninstalling it fixes the issue; install it again and the issue comes back.