Turns out the 'fault' response was incorrect. It was missing the <soapEnv:Fault>
element.
The following response now returns the correct 'exception'.
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
<soapenv:Body>
<soapenv:Fault>
<faultcode>soapenv:Server</faultcode>
<faultstring>SOAP Fault Recieved from server.</faultstring>
<detail>
<NS1:verify_fault xmlns:NS1="https://www.acme.com">
<Code>RecordNotFound</Code>
<Message>No Records Found.</Message>
</NS1:verifyCustomer_fault>
</detail>
</soapenv:Fault>
</soapenv:Body>
</soapenv:Envelope>