"Considering this little history, it's no surprise to see that jBPM 5 is a completely different workflow engine compared to jBPM 4 with a totally different API and documentation, lacking almost all the maturity and community support existing on jBPM 4"
This is quite the opposite... the Drools and jBPM community join the forces to create a very good project. That's why the project is getting very good momentum. The same as BPMN 2.
Cheers