ConcurrentModificationException in xref when run multithreaded.

This causes Jenkins to choke when in does not find a </story> for the story in question (the xunit plugin stage):

[WARNING] Failed to run story loyalty/RapidRewards_extend_awards.story
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:372)
at java.util.AbstractList$Itr.next(AbstractList.java:343)
at org.jbehave.core.reporters.CrossReference$XRefRoot.processStories(CrossReference.java:273)
at org.jbehave.core.reporters.CrossReference.createXRefRoot(CrossReference.java:115)
at org.jbehave.core.reporters.CrossReference.outputToFiles(CrossReference.java:96)
at org.jbehave.core.reporters.CrossReference$1.afterStory(CrossReference.java:206)
at org.jbehave.core.reporters.ConcurrentStoryReporter.afterStory(ConcurrentStoryReporter.java:114)
at org.jbehave.core.embedder.StoryRunner.run(StoryRunner.java:263)
at org.jbehave.core.embedder.StoryRunner.run(StoryRunner.java:163)
at org.jbehave.core.embedder.Embedder$EnqueuedStory.call(Embedder.java:686)
at org.jbehave.core.embedder.Embedder$EnqueuedStory.call(Embedder.java:650)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)