VP One Page Checkout has caching issues when only ZIP of Billing address is modified
https://open-tools.net/forum/shipping-by-rules-plugin/5296-zip-not-working-at-all.html#7705
When one only changes the ZIP code of the billing address, VP OPC makes an AJAX call, where the plugin apparently re-uses the cached rule matching of some previous call (i.e. with the old ZIP code), even though it receives the correct ZIP code in the request (using Name="ZIP={ZIP}" shows the correct, new ZIP code, as the rule name is evaluated after cached values are retrieved).