Completing User Task takes time

In the BPM, I have a user task and several service tasks following the user task. Service tasks include a task that calls SAP which can take up to a 30 sec.

When I complete the user task, the user task waits till the other subsequent service tasks (including the one that calls SAP) to complete and finally the user task gets completed.

This is causing the slowness from the UI side. When approver clicks ‘approve’ button, user has to wait 30 sec till the user task gets completed.

Why the user task waits till the subsequent service tasks to be completed? Is there a way to complete the user task before even starting the next service task?

I’m using WebMethods 8.2.1.

Thank you.
-Won