It looks like the server validation is not being applied correctly. Its validating for UK postal code when Canada postal code is chosen.
Find this function call in the code that should looks similar to this:
WAValidateZC((isset($_POST["fieldset_group_field"])?$_POST["fieldset_group_field"]:"") . "",false,false,false,true,false,1);
Replace the 3rd false with true and the true with false. It should end up looking something like this:
WAValidateZC((isset($_POST["fieldset_group_field"])?$_POST["fieldset_group_field"]:"") . "",false,false,true,false,false,1);