Process execution gets stuck

I have a process A which contains two call activities B and C. Call activitiy C contains a Human task. When I include process A in another process Z as a reusable sub process and start the process Z. After starting process Z, process execution normally goes to process A, it calls call activities B and C as expected. But after this execution is getting stuck and execution of process Z never resumes. Process instance tab of KIE workbench shows that process instances of A, B and C are completed, Process instance Z is in Active state forever. There are no exceptions. Execution of processes is just getting stuck. When I replace on of the call activities with a script task, everything works fine. When I run the JUnits everything works fine. This problem is coming only when I invoke a process from KIE workbench.