Looking at the file I can see why it would activate the sort server behavior but it should be adding the item to the cart if you click on the add to cart button and the record can be found in the rs_Vini recordset.
As a test of the add to cart functionality add this line of code just after line 316:
die("the posted item id is: " . $_POST["eCart_ITA_1_ID_Add"];);
This should let you know if the add to cart is being triggered when your press the button. If it is not then you will not see this message. Please post back and let us know the result.