I believe that the same issue applies to the quantity in cart feature on the product_info page. By which I mean that with two identical products, except for text attributes that differ, the quantity in cart is shown as 1. I am working on a 'far from clean' install so perhaps I am mistaken.

I also wonder if corresponding changes need to be made to ipn_main_handler.php ? Sort of similar to the changes required by stock by attributes.