jBPM 4.0 was released last Friday, more infos on that can be found here.

As read in the readme.html file, the two bugs I reported were fixed:

[JBPM-2319] – Finished executions are not changed to “ended” (they stay in the “active” state)
[JBPM-2340] – TaskService getTaskComments throws NullPointerException if the task is not found

Thanks guys great work!