Today I've made so much struggle with the jBPM Eclipse plugin. It was really frustrated to know that the new version jbpm-jpdl-designer-3.1.0.alpha3 has changed the xml structure of the gdp.xml, which is used to describe the relationship between process image and process description.
After thousands of tries I've find this alpha version cannot convert the process files from old versions correctly. The result is, you will lost all transition lines on the process image. So just be careful to do the update!
The issue is here: http://jira.jboss.com/jira/browse/GPD-64