We are testing sample throw and catch signal event with event data using JBPM 6.1.0 Final. We found following points...
1. In another process where start is through signal there output variable name should be 'event' to signal start second process. If output variable name is not 'event' then event data can not extracted into another process. Find code of ProcessRuntimeImpl below where 'event' is hardcoded for start signal output variable.

public class ProcessRuntimeImpl implements InternalProcessRuntime {

...

private class StartProcessEventListener implements EventListener {
...
public void signalEvent(String type, Object event) {
for ( EventFilter filter : eventFilters ) {
for ( Map.Entry<String, String> entry : inMappings.entrySet() ) {
if ( "event".equals(
entry.getValue() ) )

else

} }

startProcess(processId, params, type );
} } }

2. Above workaround related to triggering another process through signal start event with event data works with only Singleton runtime manager. For PerProcess Runtime manager, it fails to start another process.

Forum thread where related logs and BPMN files are attached
https://community.jboss.org/message/884049#884049