How to store and access per call data in WCF - asp.net

Question

I'm trying to set up some WCF services that are connected and pass a custom HTTP header from service to service.
That is my client call ServiceX, which calls ServiceY, which writes to the DB.
They are originally called from a Silverlight 5 client in some cases, other cases from an ASP.NET web app.
I implemented IClientMessageInspector and IDispatchMessageInspector to pass the header from service to service, and in the DispatchMessageInspector I wrote the header to an implementation of IExtension(Of OperationContext) (see below).
However, I wanted this data only to exist for the duration of the call, but it seems to be sticking around in the services under certain circumstances as I keep seeing the same header data repeated in different calls.
Ultimately, I want to be able to pass a custom header to a WCF service, persist it only while that call exists, send it to the next service in the header, and wipe out that service instance. Am I wrong in my thinking that using a PerCall WCF service setup and OperationContext is the right way to do that?
Here is my implementation of IExtension(Of OperationContext). The auditTransactionId is the thing I want to pass in the service. As well, the Current() property is where I keep seeing existing data:
Imports System.ServiceModel
Public Class CustomOperationContextExtension
Implements IExtension(Of OperationContext)
Private ReadOnly m_items As IDictionary(Of String, Object)
Private m_auditTransactionId As String
Private Sub New()
m_items = New Dictionary(Of String, Object)()
End Sub
Public ReadOnly Property Items() As IDictionary(Of String, Object)
Get
Return m_items
End Get
End Property
Public Property AuditTransactionId() As String
Get
Return m_auditTransactionId
End Get
Set(value As String)
m_auditTransactionId = value
End Set
End Property
Public Shared ReadOnly Property Current() As CustomOperationContextExtension
Get
If (OperationContext.Current IsNot Nothing) Then
Dim context As CustomOperationContextExtension = OperationContext.Current.Extensions.Find(Of CustomOperationContextExtension)()
If context Is Nothing Then
context = New CustomOperationContextExtension()
OperationContext.Current.Extensions.Add(context)
End If
Return context
End If
Return Nothing
End Get
End Property
Public Sub Attach(owner As OperationContext) Implements IExtension(Of System.ServiceModel.OperationContext).Attach
End Sub
Public Sub Detach(owner As OperationContext) Implements IExtension(Of System.ServiceModel.OperationContext).Detach
End Sub
End Class
EDIT:
When I say that data is sticking around, I mean that when I call Current in a new service call I expect the Extensions list to be empty (in the code below in the Current() property), but there is always an existing instance of CustomOperationContextExtension there already that is left over fro a previous call. I'm not sure under which circumstances this happens.