I think I have an issue with the activiti designer tool. When importing bpmn file containing owner fields, this one is duplicated by the eclipse activiti designer and namespace xmlns:activiti="http://activiti.org/bpmn" is added too in the task.
Example : <userTask id="TestUserTask" name="Process Manually" activiti:candidateGroups="CANDIDATES" activiti:category="CATEGORY" activitiwner="OWNER"> To <userTask id="TestUserTask" name="Process Manually" activitiwner="OWNER" activiti:candidateGroups="CANDIDATES" activiti:category="CATEGORY" xmlns:activiti="http://activiti.org/bpmn" activitiwner="IT-SUPPORT-SPARK"> After Eclipse module use and save.