See the linked bug on eclipse bugzilla.
Fixed with build 1.1.1.201411111921 available here: http://download.eclipse.org/bpmn2-modeler/updates/luna/1.1.1
jbds-8.0.1.GA_jbdsis-8.0.0.Beta2 contains BPMN2 Modeler 1.1.1.201411261859 which generates the same xml as reported modeler 1.1.0. But if I run process with jbpm 6.2.0.CR3, mapping from start message to variable works.