Sorry, this issue has took me a lot of time to reproduce it.
The bug is a combination of claim-plugin and jacoco-plugin. When someone claims for a test failure, claim-plugin serializes the MavenModuleSetBuild with the test failure. This serialization includes all the plugins that the current job have configured.
As your job have the jacoco-plugin configured, JacocoBuildAction it's serialized too. This class have a field called logger of type PrintStream that is serialized too with binary data, and this is what is breaking the xml. In a normal scenario, the PrintStream have to be empty, and this problem wouldn't happens. The logger instance is shared with the listener, and I think that other process was running and using that instance at the moment of claim the test failure.
In order to fix your build.xml, you can delete manually the entire element <hudson.plugins.jacoco.JacocoBuildAction plugin="firstname.lastname@example.org"> from D:/build/hudson/jobs/ws-kredit-kreditansoegning%20trunk%20NB/modules/dk.nykredit.kredit.kreditansoegning$kreditansoegning-service/builds/828/build.xml.
I will send a PR to the jacoco-plugin, to prevent that the logger gets serialized.