TDS group greyed out in PO - AX 2012 R3 IND localization

  1. Created a PO and received. At this point TDS group is greyed out. (Sales tax info is still editable)

  2. Updated Vendor with TDS group and PAN No. details

  3. TDS group is still greyed out for the received PO (per point 1)

Now how can I update the TDS group. Any help would be appreciated