WCF Custom SOAP Header Issues

Question

I'm trying to implement an endpoint behavior which injects a custom SOAP header into all messages to and from a service. I've gotten pretty close by implementing the approach from the accepted answer of this question:

http://stackoverflow.com/questions/986455/wcf-wsdl-soap-header-on-all-operations/995951#995951

After implementing that solution, my custom SOAP header does indeed show up in the WSDL; however, when I try to call the methods on my service, I get the following exception/fault:

<ExceptionDetail xmlns="http://schemas.datacontract.org/2004/07/System.ServiceModel" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"&gt;
      <HelpLink i:nil="true" />
      <InnerException i:nil="true" />
      <Message>Index was outside the bounds of the array.</Message>
      <StackTrace>   at System.ServiceModel.Dispatcher.DataContractSerializerOperationFormatter.AddHeadersToMessage(Message message, MessageDescription messageDescription, Object[] parameters, Boolean isRequest)
   at System.ServiceModel.Dispatcher.OperationFormatter.SerializeReply(MessageVersion messageVersion, Object[] parameters, Object result)
   at System.ServiceModel.Dispatcher.DispatchOperationRuntime.SerializeOutputs(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.DispatchOperationRuntime.InvokeBegin(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage5(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage4(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage3(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage2(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.ImmutableDispatchRuntime.ProcessMessage1(MessageRpc&amp; rpc)
   at System.ServiceModel.Dispatcher.MessageRpc.Process(Boolean isOperationContextSet)</StackTrace>
      <Type>System.IndexOutOfRangeException</Type>
    </ExceptionDetail>

Looking in Reflector at the DataContractSerializerOperationFormatter.AddHeadersToMessage method thats throwing the exception, leads me to believe that the following snippet is causing the problem...but I'm not sure why.

MessageHeaderDescription description = (MessageHeaderDescription) headerPart.Description;
object parameterValue = parameters[description.Index];

I think the last line above is throwing the exception. The parameters variable is from IDispatchFormatter.SerializeReply

What's going on?!?!!

Any help would be greatly appreciated...