VM - Custom, stockable variants plugin child discounts

[Geppux]

Hi everybody, I use Joomla 2.5.13 and VM 2.0.22a on Linux. The problem is the following: if I create a parent product and child products with VM - Custom, stockable variants plugin and I create different calcolation rules for the child products these rules are not considered! The only rule considered are the calcolation rules of the parent product.  I searched in many sites and I made many test and I haven't found a solution, it's seems a bug.
Thank you.
Giuseppe