Hi Johan,
This is caused by nested fork. And it has already be fixed in the jBPM 4.4-SNAPSHOT. You can see the issue in JIRA been marked as resolved.
https://jira.jboss.org/jira/browse/JBPM-2648
By the way, your xml is totally weired. I don't understand why you used fork/join like this. the join3 looks like useless