The encodingStyle attribute is not allowed in spyne

I try to figure out how to build a soap service with spyne to this kind of request:

<soapenv:Envelope xmlns:xsi="http://ift.tt/ra1lAU" xmlns:xsd="http://ift.tt/tphNwY" xmlns:soapenv="http://ift.tt/sVJIaE" xmlns:urn="urn:MyService">
<soapenv:Header/>
  <soapenv:Body>
    <urn:test_rpc soapenv:encodingStyle="http://ift.tt/wEYywg">
      <urn:in0>test</urn:in0>
    </urn:test_rpc>
  </soapenv:Body>
</soapenv:Envelope>

My Testmethod looks like this:

@spyne.srpc(Unicode, _return=Result, _in_variable_names={"input": 'in0'}, _body_style='wrapped')
def test_rpc(input):
  return Result()

When I send my requests the soap service respond with following Webfault:

Server raised fault: ':1:0:ERROR:SCHEMASV:SCHEMAV_CVC_COMPLEX_TYPE_3_2_1: Element '{urn:MyService}test_rpc', attribute '{http://ift.tt/1u1aMnv': The attribute '{http://ift.tt/1u1aMnv' is not allowed.' 

How can I fix this without removing the encodingStyle? The section 4.1.1 of the Simple Object Access Protocol (SOAP) 1.1 W3C Note (http://ift.tt/1u1aNaR) notes that "This attribute[encodingStyle] MAY appear on any element, ..."