A customer was observing that the BAMTaskSummary.status and Task.status were out of sync:
BAMTaskSummary.status = 'Exited'
Task.status = 'Reserved'

Upon investigation, the TaskEvent tables for the process (taskid) in question had the following entries when the task has changed ownership:
38590 05-NOV-16 10.20.02.646000000 AM 15653 DELEGATED one@acme.com 0
38591 05-NOV-16 10.20.02.650000000 AM 15653 EXITED one@acme.com 0
38603 05-NOV-16 10.19.44.547000000 AM 15653 ADDED two@acme.com 0
44908 21-NOV-16 05.08.35.999000000 PM 15653 EXITED one@acme.com 0

It was identified that BAMTaskEventListener was incorrectly updating the status to Exited:
https://github.com/droolsjbpm/jbpm/blob/master/jbpm-human-task/jbpm-human-task-audit/src/main/java/org/jbpm/services/task/lifecycle/listeners/BAMTaskEventListener.java#L140