wsdl doc has missing wsdl:port element when svcutil executed from a Process object in a windows app

Question

For reasons unnecessary to go into on this thread, I'm trying to create a wrapper for svcutil, which will then standardise the wsdl & xsd docs created to point at certain addresses. However, one of my WCF services has two different service contracts, one for internal processing, one published to external clients. When I run svcutil /target:metadata serviceAddress.svc from cmd.exe, I get a full wsdl doc with the following entry:

<wsdl:service name="MyServiceMain">
    <wsdl:port name="BasicHttpBinding_IMyService" binding="tns:BasicHttpBinding_IMyService">
        <soap:address location="MyServiceMain.svc" />
    </wsdl:port>
    <wsdl:port name="BasicHttpBinding_IInternalServiceContract" binding="tns:BasicHttpBinding_IInternalServiceContract">
        <soap:address location="MyServiceMain.svc" />
    </wsdl:port>
</wsdl:service>

However, if I use a Process object (with a ProcessStartInfo object with the same environment variables set up, definitely using the same version of svcutil) to run the same command, one of those wsdl:port elements mysteriously disappears:

<wsdl:service name="MyServiceMain">
    <wsdl:port name="BasicHttpBinding_IMyService" binding="tns:BasicHttpBinding_IMyService">
        <soap:address location="MyServiceMain.svc" />
    </wsdl:port>
</wsdl:service>

Any idea as to why? Or even something that can point me in the right direction that might indicate something different happening under the hood. Because I'm stumped right now.