Browser doesn't distinguish a partial HTML got via AJAX and a full page
Have your Ajax call use a different URL like /products/partial.
You should have a diferent url for partial results (i.e ?partial=yes or something like this...)
OR
you can get the whole page via ajax and extract just the part you want using jquery.load().
$("#productsContainerHolder").load("/my/products/url #productsContainer", { myParam: "beer", myParam2: "cold"});$.load will call your server with a 'GET' method, retrieve all contents, extract the #productsContainer from there and insert on "#productsContainerHolder"
<div id="productsContainerHolder"> <div id="productsContainer> ... </div></div>
This article by Steve Luscher describes a similar case the problem was more intermittent than what you describe. The suggested solutions are:
Cancel all of the AJAX requests at the time the form is submitted
Use a different URL according to the response you expect
Steve went for #1 using cancel() on the ajax requests.
You don't mention what browsers you have used, there is a browser related question here