The current BPMN parser falls back to the BPMN 2.0 beta XSD in case that the parsing fails.
This has been done, because at the time, the Activiti Modeler was only able to produce 'beta-compatible' process models (compatibility with the final XSD was promised to be done in August).
So this issue includes:
verify compatibility of the Activiti Modeler
remove fallback to BPMN 2.0 beta XSD
remove the Beta1SignavioCompatibility test class