In the screen shots that you posted the name of the form variable should be eCart1_1_ID_Add, this is what I meant but I used the term value instead. When you test it for the test value you would use any valid id from that table.
I did some testing of this functionality and can confirm that it seems to be working correctly. Mine is setup a little different that yours is though. Here is what I did. I first added the recordset to the page. Next I added the add to cart button from the eCart insert bar. I choose the lookup item from recordset option, then in the bindings tab I bound the cart column with the corresponding column from my recordset. Once that was finished I highlighted the form on the page and added a repeat region.
When I had mine setup like this click on the add to cart button for any of the items got the correct item to be added to the cart.