Process Manufacturing same item two line of issue

Hi,

There is Scenario where I have created work Order for Item A

I have Row Material for that as Item B

But in Co product i have got Item C and D for which i have defined Feat cost  as 45 and 55 in P3003  and resource Percentage as 0 and 100 

Now as we are using back flush at the Row material issue screen it appear as two line of same item which is not require

kindly suggest how we can have a single line for item B at the time of row Material issue

Thanks,