How to merge product in show cart if custom filed is altered

[ramchandev]

Hi

I am using VM 2.0.10 and joomla2.5 as my base. I have added the "textinput" plugin as my custom filed attribute to a product. Every thing worked fine, but the problem is when I add this product to the cart. If I have to edit the text that I have entered for the engrave(textinput custom filed) option then I click the product link from the show cart page. It takes me back to the product detail page if I update the "textinput" text and click "Add to cart" then it puts as new product in my cart.

Can some one please point me or help me to solve this, to update the custom filed and in the same product, I do not want the product to add as a new product.

Thanks in advance
Ram