When the Simple Theme Plugin is installed, configure pages for both jobs and Jenkins itself hang at the "LOADING" overlay (as seen in https://issues.jenkins-ci.org/browse/JENKINS-16165). Furthermore, configurations cannot be saved, as hitting the "save" button with the plugin installed will result in a "HTTP ERROR 400" page (see second attachment).