VAT / EU calculation error

I am upgrading from Spark version 5 to version 9 as I need the latest version of Cashier. I have collectEuropeanVat enabled and I am using the mpociot/calculator.

On the sign-up form for a customer from an EU country (e.g Austria), the form correctly calculates the VAT due at that countries rate, however when the VAT ID is entered, the VAT amount is not updated. It should move to $0 when a customer is VAT registered and enters their ID.

It worked correctly in version 5, but appears broken on my test version 9. Is this a bug or am I missing something?