Grrr, IE. Why do I always leave the testing of that browser for the end?

Turns out that the checkout_one page's form doesn't submit properly on IE (IE-11, at least) and just redisplays the checkout_one page on submit-key click.

The issue is that by disabling the HTML <div> in which the submit-button resides on-click, IE disables all the hidden-input variables in that section as well, so the plugin's confirmation page doesn't "see" that it was a real form-submit and redirects back to the main checkout page.

That said, a two-line change to /includes/modules/pages/checkout_one/jscript_main.php is required (it'll be staged for v1.0.2 in the plugin's GitHub repository). Towards the bottom of the file, find:
Code:
    $('form[name="checkout_payment"]').submit(function() {
        zcLog2Console ('Form submitted, orderConfirmed ('+orderConfirmed+')');
        if (orderConfirmed) {
            $('#checkoutOneSubmit').attr('disabled', true);
<?php 
if ($flagOnSubmit) { 
?>
            var formPassed = check_form();
            zcLog2Console ('Form checked, passed ('+formPassed+')');
            if (formPassed == false) {
                $('#checkoutOneSubmit').attr('disabled', false);
            }
            return formPassed;
<?php 
} 
?>
        }
    });
and make the two highlighted changes:
Code:
    $('form[name="checkout_payment"]').submit(function() {
        zcLog2Console ('Form submitted, orderConfirmed ('+orderConfirmed+')');
        if (orderConfirmed) {
            $('#confirm-order').attr('disabled', true);
<?php 
if ($flagOnSubmit) { 
?>
            var formPassed = check_form();
            zcLog2Console ('Form checked, passed ('+formPassed+')');
            if (formPassed == false) {
                $('#confirm-order').attr('disabled', false);
            }
            return formPassed;
<?php 
} 
?>
        }
    });