NAV 2013 Calculate Rolled-up Material Cost

Hi all,

I have a problem / question regarding the calculation of standard cost in NAV 2013:

Item A is a finished good with costing method standard. It has no routing and a production BOM with only one item, item B (raw material, costing method average). I use the standard cost worksheet to calculate the standard cost of item A.

Last calculation item B had unit cost of 100, standard cost of 100 and rolled-up material cost of 100. So after the calculation, item A also had
standard cost of 100 and rolled-up material cost of 100.

In the meantime unit cost of item B changed to 120. Now I use the standard cost worksheet again to calculate the standard cost of item A. The new standard cost and new rolled-up
material cost of item A is calculated to 120. Fine.

BUT:
I also want to update the standard cost and rolled-up material cost of item B. No matter how I try, it always stays 100.

This causes a problem i.e. in the report rolled-up cost shares. Here item B has material cost of 100 and in the total item A has material cost of 120. The difference cannot be
explained so easily.

Am I doing something wrong? Is there a way to handle this properly in NAV 2013? Or does this have a reason?

Thanks in advance

MiSta78