Service tasks with expressions does not propagate errors

When a service task is using activiti:delegateExpression and it throws a BpmnError, this error is not propagated. This means, the service task ignore the boundary event error.

To reproduce this bug, unzip the attached file inside the activiti-spring project and execute the test case org.activiti.spring.test.servicetask.BoundaryErrorEventSpringTest.
This test is the same as org.activiti.engine.test.bpmn.event.error.BoundaryErrorEventTest.testCatchErrorThrownByJavaDelegateOnServiceTask() in activiti-engine but using delegate expression in a service task.