Item branch primary supplier number is changing

We are experiencing item branch primary supplier number changing when we have purchase order that we source from multiple suppliers. It seems that when we use receipt routing and receives material and move to stock (STK), at this time primary supplier number on the item branch is changing to the supplier number on the PO receipt when moved to stock in the receipt routing. For example, if item branch has primary supplier number of 1 but we have a receipt of the same item where supplier number is 2, after the move to STK, the item branch primary supplier number