Great Point Jurgen... I have delete PO, re-ran MRP and review the results. System is picking vendor : 14138 which is correct. Seems like when we convert PR to PO system is not allowing because now it's checking PO delivery date with source list validity date and gives error "Source not included in list despite source list requirement". Due to that error users was changing PO vendor to 15251 .
Resolution is we have de-activated "Source list" flag from material master so system does not give hard code error.
Thanks !!!
Regards,
Ravi.