The payment clause of a sales contract between Company A(the seller) and Company B(the buyer)stipula10% of the total value of the goods should be put in advance to the seller's account before September 10th.Within 20days after receiving the down payment,the seller effects shipment,sending one copy of the B/L to the buyer who in turn puts the rest of the payment to the seller's account in exchange for original B/L.However,the buyer demanded the seller

The payment clause of a sales contract between Company A(the seller) and Company B(the buyer)stipula
10% of the total value of the goods should be put in advance to the seller's account before September 10th.Within 20days after receiving the down payment,the seller effects shipment,sending one copy of the B/L to the buyer who in turn puts the rest of the payment to the seller's account in exchange for original B/L.However,the buyer demanded the seller put the buyer's name to the consignor on the B/L.The trade term involving in the contract was FOB Shanghai.The seller effected shipment on September 24th,18 days after receiving the 10% goods values remitting from the buyer and sent one copy of the B/L to the buyer as stipulated in the contract.However,although the seller pressed for the payment again and again,the buyer always tried to delay.The seller then asked the carrier not to release the goods to the buyer.However,the carrier told the seller the buyer had taken away the goods with the copy of the B/L for he was the consignor on the B/L.
Questions for discussions:
1.Why did the seller keep the original B/L before getting the full payment in FOB contract?
2.Why could the buyer take delivery without original B/L in this case?