Actually, I found again a situation which is described to the one above which does not work with the patch given in JIRA issue 2922 (see https://issues.jboss.org/browse/JBPM-2922). I tested it with the patch I made and it worked without any problems. Thus, I suggest to use my patch (see post no. 4 above). Nevertheless, it would be still great to discuss whether my solution is appropriate or not to fix the problem.