Product Costing - CK11N BOM component wrong quantity

Hi,

I have a question regarding Material Cost Estimates. I have a material (Product A) which has a BOM header Qty of 524. One of the Components (Product B) has a Qty of 560. When I run the Cost Estimate for Product A, the component costing list doubles the quantity of Product B, and therefore doubles the cost (this is when I change the report Qty to 524).

The Costing Lot Size on the product A is 1. When I change this Costing Lot Size on the material master to 100 and rerun the CK11N, the Component Qty and Cost are correct.

Is there some rule that I should be following when it comes to Costing Lot Sizes?

Thanks for any help.

Daniel.