[GSS][6.3.z]Error signaling a subprocess using the EJB API

+++ This bug was initially created as a clone of Bug #1330191 +++

Description of problem:

We have a Web application that makes use of the jbpm EJB remote API. The web application will handle a process that right after a task is complete, a subprocess is started and it has a signal event;
In the web application and using the ProcessServiceEJBLocal, RuntimeDataServiceEJBLocal and UserTaskServiceEJBLocal, it will do the following in a method of a stateless EJB (that has the mentioned jbpm EJBs injected)

• complete the task
• find the subprocess instance id
• send a signal to the subprocess

The subprocess instance ID is found correctly, but when sending the signal, we have an exception saying that the process can't be found.

Version-Release number of selected component (if applicable):

n/a

How reproducible:
always

Steps to Reproduce:
1. Create a process that has a task and then a subprocess that waits for a signal
2. In an application that uses the EJB API, start the process and the task from an EJB in a method
3. In the other method, complete the task and try to signal the process instance id
(the attached reproducer clarifies the issue)

Actual results:

Exception:

Expected results:

11:52:45,403 ERROR [org.jboss.as.ejb3.invocation] (http-/127.0.0.1:8080-1) JBAS014134: EJB Invocation failed on component ProcessServiceEJBImpl for method public abstract void org.jbpm.services.api.ProcessService.signalProcessInstance(java.lang.Long,java.lang.String,java.lang.Object): javax.ejb.EJBTransactionRolledbackException: Process instance with id 4 was not found

Subprocess signaled with success.

Additional info:

Reproducer is attached. Read the reproducer README.md before running it.

— Additional comment from JBoss Product and Program Management on 2016-04-25 11:00:09 EDT —

Since this issue was entered in Red Hat Bugzilla, the release flag has been
set to ? to ensure that it is properly evaluated for this release.