As far as I knew, eBay has never added the $9 surcharge into postage costs to the US when using calculated - I don't post OS so I'm only basing that on previous threads about this issue, and the solution I've mentioned above is the only way I know of that guarantees US buyers are charged the fee but no one else is.

If the $9 surcharge was being added to the P&H total previously and isn't now (with no changes being made to your listings), that suggests it's something eBay need to resolve so without wanting to adopt the method I've mentioned, I don't think there's a solution other than waiting for eBay to fix.