The calls to form_set_error in uc_restrict_shipping_validate() do not specify form elements.

This in itself is not a bug because that is allowed but if other modules are already doing the same thing you won't get your message displaying until the other modules errors are resolved.

With a form like the checkout form this is an issue because there is the potential for so many other modules to be adding their own validation that could interfere.

This is because form_set_error will only set one error per element.

So it would be better from the user's point of view that elements be specified so they see all their errors.