False Unit ((ProdCalcTrans).Key2) in the Production Calculation

Good morning together,

We´ve got the following problem in Dynamics AX 2009:

- We produce article A

- article A has got article B in our variant parts list (BOM) with unit "mm" (millimeter)

- article B has storage unit "piece"

- article B has got a unit translation from mm to piece: 2000 mm = 1 piece

- in the production BOM for article A, article B is contained with unit "mm" --> 900 mmm = 0,45 piece

- problem: in the production calculation article B is not includ, because the unit is "piece" and AX is rounding the value: 0,45 piece = 0 piece

Does anybody know, why article B gets in the production calculation with the storage unit "piece" and not with the unit of the BOM (=mm)?