Description of problem: See linked issue.
This issue is still reproducible. Please see https://bugs.eclipse.org/bugs/show_bug.cgi?id=431555#c8.
Still reproducible on: jbds-9.0.0.CR2_jbdsis-9.0.0.Alpha2 BPMN2 Modeler - 1.2.1.201509111741
This looks like it's only reproducible on Linux. Windows systems do not have this problem. The workaround is to first ensure all BPMN2 editors are closed, then open the Outline View and then open the BPMN2 editor. Closing this because a workaround exists.