Several clients have experienced problems when trying to save changes when editing their products in some versions of Prestashop 1.6.X. They edit the product, save changes and everything seems correct, but the changes are not visible on the frontend or in the product file edition in the backend if you go back in. Generally, this problem happens if the Chrome browser is used, but we have also found cases where it happens with other browsers.

Dear customer,
Please go to this file within your Prestashop:
/adminXXXX/themes/default/template/controllers/products/helpers/form/form.tpl
Within this file you must search for:

submitHandler: function(form) {
form.submit();
},

And replace it with:

//submitHandler: function(form) {
//form.submit();
//},

And then try to see if your Prestashop 1.6 correctly performs all the changes.