Inventory account showing " 0 " during 161 movement type

Dear Experts,

Request for valuable inputs.

Issue: Return PO has been created for the same material ( example: A00000000 - Price control is V ) in two different line items, but one line item              is with CS and second line item in PC. Performed MIGO ( 161 - Movement type ). When we checked in MB51, we observed that article                      document got posted with " 0 " value in Inventory account for the second line item and that value is added in the 1st line item inventory                      account.

Example is as below

But if you go to Accounting documents, entries are as below.

for the two line items.

Inventory account = 29.317,21-

GR/IR Account = 31.405,68

PRD = 2.088,47-

GR/IR account = 408,27

PRD = 408,27-

Please advise why value " 0 " is coming in MB51.

Regards

Sesha.