Purchasing Mismatch when creating PO with Ref to RFQ

Hello Gurus,

when creating a PO with Ref to RFQ, Purchasing group mentioned in the RFQ is not appeared in the PO. In PR & RFQ different Pur. Group is maintained, but when PO is created its showing some other Pur Group.

Kindly suggest me how & why this happend.

Thanks in advance.