Forms 9.1.1 resolved an issue where Laserfiche Forms was not correctly pre-populating read-only fields with field variables (e.g., current user). 

If you are populating read-only fields after the form loads, Forms will not store that value as a security precaution. This is the intended behavior.

In some cases it makes sense to work around this issue by using JavaScript to make the field read-only after the form loads. For example, you could try making the field read-only after it has a value as part of your sumtotal function. Add the ro class to the field you want to make read-only.

Once the value is populated on the initial form, it will become read-only (because it is part of a code block that runs when the user leaves a table field). But if the form is opened again in a user task or when being saved to the repository, the field won't automatically be read-only (because when the form opens, the user hasn't left that table field yet).

$(document).ready(function () {

    $('.cf-table-block').on('blur', 'input', sumtotal);

    function sumtotal() {
        var sum = 0;
        $('td.sum').each(function () {
            var s = 0;
            $(this).find('input').each(function () {
                s += parseNumber($(this).val());
            })
            $(this).find('.subtotal input').val(s);
            sum += s;
        });
        $('.total input').val(sum);

        $('.ro input').attr('readonly', 'True'); //makes the field read only after we give it a value.

    }

    function parseNumber(n) {
        var f = parseFloat(n); //Convert to float number.
        return isNaN(f) ? 0 : f; //treat invalid input as 0;
    }

});