Hi Maciej,
I read about Developers Guide.
http://docs.jboss.com/jbpm/v4/devguide/html_single/#groupsecret
Seems that Tom didn't want to let a transition jump from a group to another group.
But how could we handle it now? Do we need implement the feature like jBPM 3? Or limit the behaviour of transitions in groupActivity, not let them go over the boundary of GroupActivity?