Hi Poonam
"In the last task of the workflow where VBD document is getting released"
is it a background task? If yes, the event would show user WF-BATCH and you can easily bypass triggering of the workflow using a start condition checking Workflow Initiator <> USWF-BATCH.
If it is not a background task, then it gets executed by the user who executes the work item. Then we will need more information on the event triggering technique used - is it by way of enhancement and coding or some other process is followed?
Regards,
modak