Roll up of inventory numbers

I love the fact that HikaShop allows me to manage my inventory at the level of the characteristics. However, if I have the following characteristics along with associated inventory count:

Black - Small 3
Black - Medium 4
Black - Large 5
White - Small 1
White - Medium 2
White - Large 0

This means I have 15 of this item. I believe these numbers should total up and insert into the inventory count for the actual product itself. Right now I have to manually enter a number there.