Free Shipping --- Your available shipping options have changed

This is a new install of 1.5 using the test store items. No modifications.

Shipping modules: freeshipper (sort order 0) & zones (sort order 10)

Order total modules: ot_shipping set to Allow Free Shipping - true; Free Shipping For Orders Over - $60.00; Provide Free Shipping For Orders Made - both

Add items to your cart so the total is over the amount set for free shipping.

Begin checkout - proceed past step one

Go back to checkout Step 1 of 3 - Delivery Information

A big red alert appears: Your available shipping options have changed. Please re-select your desired shipping method.

This alert did not happen in 1.39.

This is not exactly a bug, but rather an undesirable test that the Free Shipping on the ot_shipping triggers ...

You can avoid that message by changing the code in the file:
/includes/modules/pages/checkout_shipping/header_php.php

    $checkval = (is_array($_SESSION['shipping']) ? $_SESSION['shipping']['id'] : $_SESSION['shipping']);
    if (!in_array($checkval, $checklist) && $_SESSION['shipping']['id'] != 'free_free') {
      $messageStack->add('checkout_shipping', ERROR_PLEASE_RESELECT_SHIPPING_METHOD, 'error');
    }

NOTE: this is not an ideal solution as there could be customizations made where things on checkout_payment or checkout_confirmation might make the Free shipping from the Shipping ot_shipping invalid and then one would want the message ...

Thanks - that code change well for me.

I get nervous when I see those red alerts, and I imagine my customers might get nervous too. Maybe a yellow alert with the wording - "Your available shipping options may have changed"

For that you could change the messageStack to:

      $messageStack->add('checkout_shipping', ERROR_PLEASE_RESELECT_SHIPPING_METHOD, 'caution');

and change the define for:
ERROR_PLEASE_RESELECT_SHIPPING_METHOD