Sometimes waitForCompletion times out, and the log shows that two copies of the WorkflowRun are loaded.
Running against 1.606-SNAPSHOT, I observed an (unreproducible) failure:
java.lang.AssertionError: tried to overwrite demo #1 with demo #1
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:472)
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:448)
at jenkins.model.lazy.AbstractLazyLoadRunMap.getByNumber(AbstractLazyLoadRunMap.java:356)
at jenkins.model.lazy.AbstractLazyLoadRunMap.search(AbstractLazyLoadRunMap.java:332)
at jenkins.model.lazy.AbstractLazyLoadRunMap.newestBuild(AbstractLazyLoadRunMap.java:274)
at jenkins.model.lazy.LazyBuildMixIn.getLastBuild(LazyBuildMixIn.java:240)
at org.jenkinsci.plugins.workflow.job.WorkflowJob.getLastBuild(WorkflowJob.java:199)
at org.jenkinsci.plugins.workflow.SingleJobTestBase.rebuildContext(SingleJobTestBase.java:70)
at org.jenkinsci.plugins.workflow.WorkflowTest$22.evaluate(WorkflowTest.java:663)