When a new currency is added the user has no way to change the smallestAccountFraction, smallestCashFraction and partsPerUnit attributes. The only way this can be done is by editing the storage file. Reproducible: Always
One use-case for that is adding the currency BTC (bitcoin) were smaller fractions are required and which which does not exist in Kmymoney as of 4.7.2. A manual work around for those googling this issue: Edit the .kmy XML file and change the properties saf, ppu and scf in the <CURRENCY> Tag for BTC from 100 to somehting larger like 100000000.