Line type B issue

Dear,

I created the Purchase request by using a line type B and I put the qty 1 but lumpsum amount is 150. the problem is that when I genrate the PO by amount like insted of 150 I put 100 and genrate the PO then system update the status code by the detial lines cannot showing with remaining but I check in the p4311 table the open amount is hsoiwn 50. Please advise