Все, нашел!
На стороне WCF в web.config есть такая запись:
<service name="WcfService1.Service2">
<endpoint address="myserver:8088/Service2.svc" binding="customBinding" bindingConfiguration="WcfService1.Service2.customBinding0" contract="WcfService1.Service2" />
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
</service>
так вот, в ней полный адрес — лишний!
Подставил пустую строку:
<service name="WcfService1.Service2">
<endpoint address="" binding="customBinding" bindingConfiguration="WcfService1.Service2.customBinding0" contract="WcfService1.Service2" />
<endpoint address="mex" binding="mexHttpBinding" contract="IMetadataExchange" />
</service>
и заработало.