When running FitNesse-tests from the Jenkins-plugin, I get the following in console-output:

Starting new Fitnesse instance...
[.] $ /usr/java/latest/bin/java -jar /var/lib/jenkins/jobs/Run-FitNesse-tests/workspace/fitnesse-standalone.jar -d /var/lib/jenkins/jobs/Run-FitNesse-tests/workspace -r root -p 7100
FitNesse (v20130530) Started...
port: 7100
root page: fitnesse.wiki.FileSystemPage at /var/lib/jenkins/jobs/Run-FitNesse-tests/workspace/root
logger: none
authenticator: fitnesse.authentication.PromiscuousAuthenticator
page factory: fitnesse.responders.PageFactory
page theme: fitnesse_straight
page version expiration set to 14 days.

Connnecting to http://localhost:7100/TestSuite?suite&format=xml&includehtml
Connected: 200/OK
Force close of input stream.
Xml results saved as UTF-8 to /var/lib/jenkins/jobs/Run-FitNesse-tests/workspace/fitnesse.xml
Reading results as UTF-8 from /var/lib/jenkins/jobs/Run-FitNesse-tests/workspace/fitnesse.xml
Parsing results...
javax.xml.transform.TransformerException: javax.xml.transform.TransformerException: com.sun.org.apache.xml.internal.utils.WrappedRuntimeException: Verarbeitungsanweisungsziel, das "[xX][mM][lL]" entspricht, ist nicht zulässig.
(Stacktrace removed)

The content of the output fitnesse.xml indicates that no tests were executed:

<?xml version="1.0"?>
<testResults>
<FitNesseVersion>v20130530</FitNesseVersion>
<rootPath>TestSuite</rootPath>

<finalCounts>
<right>0</right>
<wrong>0</wrong>
<ignores>0</ignores>
<exceptions>0</exceptions>
</finalCounts>
<totalRunTimeInMillis>0</totalRunTimeInMillis>

</testResults>

<?xml version="1.0"?>
<testResults>
<FitNesseVersion>v20130530</FitNesseVersion>
<rootPath>TestSuite</rootPath>

<finalCounts>
<right>0</right>
<wrong>0</wrong>
<ignores>0</ignores>
<exceptions>0</exceptions>
</finalCounts>
<totalRunTimeInMillis>0</totalRunTimeInMillis>

</testResults>

<?xml version="1.0"?>
<testResults>
<FitNesseVersion>v20130530</FitNesseVersion>
<rootPath>TestSuite</rootPath>

<finalCounts>
<right>0</right>
<wrong>0</wrong>
<ignores>0</ignores>
<exceptions>0</exceptions>
</finalCounts>
<totalRunTimeInMillis>1162</totalRunTimeInMillis>

</testResults>

(The repetition is as it appears in the file)

When I use exactly the same command to start FitNesse as the jenkins user and access exactly the same URL to run the tests, they run correctly. Similarly, when I run FitNesse by hand and then start the job, the tests also run correctly. This problem only appears when the plugin runs the server itself.