Hello,
"we have noticed that if the initiator and the approver are same, workitem is not going to the approver, instead it is routing to WF-BATCH."
That may have been set on purpose. The approver should not be the same as the initiator. Perhaps the wf developer wanted to forward it to the WF Admin in that case and it was mistakenly set to WF-BATCH.
regards
Rick Bakker