Our third party Web Server, which has XSS filter enabled, is preventing the icons for Java Warnings, Checkstyle, FindBugs and PMD links from displaying properly. This is because there is a double slash in the icon's URL:

http://mybuildserver/jenkins/static/7c13bfa8//plugin/warnings/icons/java-24x24.png
http://mybuildserver/jenkins/static/7c13bfa8//plugin/checkstyle/icons/checkstyle-24x24.png
http://mybuildserver/jenkins/static/7c13bfa8//plugin/findbugs/icons/findbugs-24x24.png
http://mybuildserver/jenkins/static/7c13bfa8//plugin/pmd/icons/pmd-24x24.png

I am able to display the icons in the Internet Explorer if I remove the extra slash from the URL.