Looking at JIRA there are multiple open issues for 5.1: https://issues.jboss.org/browse/JBPM/fixforversion/12315098
Issue JBPM-3015 is important to me and realistically has more to do with the Drools underpinning of jBPM. I don't think this is news to the assignee since a similar bug has been assigned to the same individual on the Drools side.
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Dave