Without adding rate in supplier portal it will take the default item rate why this?

Hello team,
I have create one request for quotation for 2 item and submit it . supplier can login with his portal …for 1st item supplier can add rate and second item he can not add the rate submit the request for quotation …after that in second item it will take automatic item rate …why this happening …why this will take the default rate of item if supplier has not add the rate
Can any one help me for the same