I just tested with jbpm 5.1 installer using all defaults (which includes 1.0.0.052 designer). Ran ant install.demo and ant start.demo then uploaded both Evaluation.bpmn and Evaluation2.bpmn from the jbpm-examples module. I am able to view and save the processes without any issues..and am also able to create new processes.
Tried debugging the javascript error you said you were getting in stencilsets.js. The exception you are getting really should not happen..this is really weird because I am not sure how to reproduce the problem.
Thanks.