Co-Parts costing

Hi
I am using the co-parts functionality. My method is concurrent. I have three co-parts and I put the costing factors for labor and material this way:

Co part material #1 : 2
Co part material #2 : 0
Co-Part material #3 :1

When I receive the goods in stock, and check my costing, it puts the costing this way:

Co part material #1 : 329.80$
Co part material #2 : 164.90
Co-Part material #3 :164.90

The total is correct but I need the material 2 at zero like in the cost re partition.

Is there somebody that has experience with co-parts that could help me out to achieve zero cost.

Thanks in advance