As per http://thread.gmane.org/gmane.comp.java.hudson.user/8473, some more
additional info:

• no file pattern is specified in the project configuration
• I get PMD: 156 warnings in 94 files, but when i got to the workspace
  filesystem and do "find . -name pmd.xml | wc -l" i get 188 files.
• The graph seems to be counting differently: there i've got only about 80 warnings
• The plugin is configured in maven like this (in the reporting section):
  <plugin>
  <artifactId>maven-pmd-plugin</artifactId>
  <configuration>
  <targetJdk>1.5</targetJdk>
  <excludes>
  <exclude>**/*Test.java</exclude>
  </excludes>
  </configuration>
  </plugin>
• my maven build is invoked with mvn clean install pmd:pmd
• when i look in the build log, i see that PMD parses both target/pmd.xml and
  target/site/pmd.xml , which is probably the cause of the duplication.