Product duplicated in cart

I have a product with variable choices(stockable), Colors and Sizes.

Here's the problem, everytime i add the product with same color and size to the cart, it will duplicate instead combining both together. Refer to the attached image below, both items are same SKU, same size but they will not combine together.

For me this is VirtueMart not template issue, but please switch template to 'beez' and check result on default Joomla! template. If the problem still exist you should ask your question on VM support forum.