Product in Cart Issue

[jeliash]

I have read virtuemart forums for days and could not find any answers. Please help me.

I have a product (a shirt), when I add to cart the size "3XL" from the dropdown menu it adds 1 item to the cart. But when I go back to the same product and add the same size again it doesn't update the cart to "Quantity: 2", instead it adds the product to the cart separately. So It shows:

Product - Quantity 1
Product - Quantity 1

Instead of:
Product - Quantity 2

I would appreciate any help, thank you.

I am using Joomla! 2.5.6 and VM2.0.6

I attached a picture for your reference.

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