When the Jenkins site is accessed via short name, e.g.: http://jenkins instead of http://jenkins.domain.tld, the "Click here to forcibly terminate running steps" link fails silently. Opening the developer tools in the browser and checking the console shows the following error in Chrome:

XMLHttpRequest cannot load http://jenkins.domain.tld:8080/job/${ProjectName}/branch/${BranchName}/9/term. Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://jenkins:8080' is therefore not allowed access. The response had HTTP status code 405.

If this behavior can't be "fixed" (one could argue it's not broken), notifying the end-user of the error and referring them to the URL specified in the JENKINS_URL variable seems like a potential improvement.