Problem with scrap factor

tuhoang

Dear all experts!!!
Our customer require from system allows to define two scrap factor for one inventory item for following purpose
1. Issues scrap (This factor be used during perform consumption or issues material)
2. Purchase scrap (This factor be used during perform planning)

I have developed a customize field for user to define issues scrap, this factor is used when user perform issues material from consumption journal screen. And purchasing scrap user is defined at BOM screen and using standard function from system.
Problem I meet here is remaining quantity field alway has value <> 0 because expected quantity field and consumed quantity are not match, therefore, planning alway consider this field as a demand. (Be noted that, consumed quantity using issues scrap)
Please help me if anyone know how to define two scraps factor for one inventory item or resolve problem related to remaining quantity that mentioned as above
Many thanks and regards
Tu