why does soapserver always returns a null object?

hi,

i am trying to implement a web service using php. it should return a
complex type, but it is always null.

i have the following wsdl:
<?xml version="1.0" encoding="utf-8"?>

<wsdl:definitions xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
xmlns:tm="http://microsoft.com/wsdl/mime/textMatching/"
xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/"
xmlns:mime="http://schemas.xmlsoap.org/wsdl/mime/"
xmlns:tns="http://www.test.co.uk/soap/"
xmlns:s="http://www.w3.org/2001/XMLSchema"
xmlns:soap12="http://schemas.xmlsoap.org/wsdl/soap12/"
xmlns:http="http://schemas.xmlsoap.org/wsdl/http/"
targetNamespace="http://www.test.co.uk/soap/"
xmlns:wsdl="http://schemas.xmlsoap.org/wsdl/">

<wsdl:types>

<s:schema elementFormDefault="qualified"
targetNamespace="http://www.test.co.uk/soap/">

<s:element name="func">

<s:complexType>

<s:sequence>

<s:element minOccurs="0" maxOccurs="1" name="a"
type="tns:thing" />

</s:sequence>

</s:complexType>

</s:element>

<s:complexType name="thing">

<s:sequence>

<s:element minOccurs="0" maxOccurs="1" name="a"
type="s:string" />

</s:sequence>

</s:complexType>

<s:element name="funcResponse">

<s:complexType>

<s:sequence>

<s:element minOccurs="0" maxOccurs="1" name="funcResult"
type="tns:thing" />

</s:sequence>

</s:complexType>

</s:element>

</s:schema>

</wsdl:types>

<wsdl:message name="funcSoapIn">

<wsdl:part name="parameters" element="tns:func" />

</wsdl:message>

<wsdl:message name="funcSoapOut">

<wsdl:part name="parameters" element="tns:funcResponse" />

</wsdl:message>

<wsdl:portType name="testSoap">

<wsdl:operation name="func">

<wsdl:input message="tns:funcSoapIn" />

<wsdl:output message="tns:funcSoapOut" />

</wsdl:operation>

</wsdl:portType>

<wsdl:binding name="testSoap" type="tns:testSoap">

<soap:binding transport="http://schemas.xmlsoap.org/soap/http" />

<wsdl:operation name="func">

<soap:operation soapAction="http://www.test.co.uk/soap/func"
style="document" />

<wsdl:input>

<soap:body use="literal" />

</wsdl:input>

<wsdl:output>

<soap:body use="literal" />

</wsdl:output>

</wsdl:operation>

</wsdl:binding>

<wsdl:binding name="testSoap12" type="tns:testSoap">

<soap12:binding transport="http://schemas.xmlsoap.org/soap/http" />

<wsdl:operation name="func">

<soap12:operation soapAction="http://www.test.co.uk/soap/func"
style="document" />

<wsdl:input>

<soap12:body use="literal" />

</wsdl:input>

<wsdl:output>

<soap12:body use="literal" />

</wsdl:output>

</wsdl:operation>

</wsdl:binding>

<wsdl:service name="test">

<wsdl:port name="testSoap" binding="tns:testSoap">

<soap:address location="http://localhost/test.php" />

</wsdl:port>

<wsdl:port name="testSoap12" binding="tns:testSoap12">

<soap12:address location="http://localhost/test.php" />

</wsdl:port>

</wsdl:service>

</wsdl:definitions>


i then have the following php script:
<?php

class thing
{
public $a;
}

class test
{
public function func($a)
{
$a->a = "returning";
return $a;
}
}

$wsdl = "test.wsdl";

ini_set("soap.wsdl_cache_enabled", "0");
$server = new SoapServer( $wsdl, array('soap_version' => SOAP_1_2));

$server->setClass("test");
$server->handle();

?>

however, whatever i pass to the web method i get:
<?xml version="1.0" encoding="UTF-8"?>
<SOAP-ENV:Envelope
xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/"
xmlns:ns1="http://www.test.co.uk/soap/">
<SOAP-ENV:Body>
<ns1:funcResponse/>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>

ie. funcResponse is null.

i'm sure i'm missing something simple so any help would be much
appreciated.

many thanks,
mike.