Addressing has a hidden requirement that force an endpoint to fail with a custom exception when it encounters duplicate addressing headers:

<soap11:Envelope xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://www.w3.org/2005/08/addressing">
<soap11:Header>
<wsa:To>http://example.org/node/A</wsa:To>
<wsa:Action>http://example.org/action/echoIn</wsa:Action>
<wsa:Action>http://example.org/action/echoIn</wsa:Action>
<wsa:MessageID>urn:uuid:D447F2F4-9980-4012-93A4-5F0C9F7630ED</wsa:MessageID>

</soap11:Header>
<soap11:Body>
<m:echoIn xmlns:m="http://example.org/echo">Echo This Text</m:echoIn>
</soap11:Body>
</soap11:Envelope>

<soap11:Envelope xmlns:soap11="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wsa="http://www.w3.org/2005/08/addressing">
<soap11:Header>
<wsa:Action>http://www.w3.org/2005/08/addressing/fault</wsa:Action>
<wsa:FaultDetail>
<wsa:ProblemHeaderQName>wsa:Action</wsa:ProblemHeaderQName>
</wsa:FaultDetail>
<wsa:MessageID>urn:uuid:0293E1C3-3C60-455C-820A-CDF70D0795D1</wsa:MessageID>

<wsa:RelatesTo>urn:uuid:D447F2F4-9980-4012-93A4-5F0C9F7630ED</wsa:RelatesTo>
</soap11:Header>
<soap11:Body>
<soap11:Fault>
<faultcode>wsa:InvalidAddressingHeader</faultcode>
<faultstring xml:lang="en">A header representing a Message Addressing Property is not valid and the message cannot be processed</faultstring>
</soap11:Fault>

</soap11:Body>
</soap11:Envelope>