Hi Blod,
Here you have more details:
http://help.sap.com/saphelp_ewm70/helpdata/en/c5/c4703736bfb37de10000009b38f8cf/frameset.htm
To determine the procurement quantities of the PP/DS orders from the receipt quantity of an SNP or CTM order, PP/DS performs a procurement quantity calculation during the conversion (“lot formation”).
You have various options in this situation. You could perform a 1:1 conversion or an SNP-independent redetermination of the procurement quantities using the lot size settings from the location product master. For more information, see 
Procurement Quantity Calculation for SNP-PP/DS Conversion.
Regards, Marius