C# :: WCF Duplex Service Callback Channel Hanging

I have an application based around a WCF Duplex service. I have problems when the user "Restarts" the work the application does... under the hood, the client side closes the connection to the WCF service and creates another. The Service contract is defined like so...

[ServiceContract(Namespace="net.tcp://namespace.MyService",
SessionMode=SessionMode.Required,
CallbackContract=typeof(IServiceCallback))]
public interface IMyService {
[OperationContract(IsOneWay=true)]

[Code] ....

The issue I see is that the _context.Close() call always times out and throws an exception. Although I'm then aborting the channel, this feels wrong to me, and I believe it's the cause of freezing in my application. Why the Close() call fails?

I missed something earlier regarding my callback implementation that might be relevant. It looks something like this:

[Callbackbehavior(ConcurrencyMode = ConcurrencyMode.Single,
UseSynchronizationContext = false,
IncludeExceptionDetailInFaults = true)]
public class CallbackImplementation : IServiceCallback {
public void SendMessage(string message){
// Do something with the message
} }

The exception message is "The ServiceHost close operation timed out after 00:00:30. This could be because a client failed to close a sessionful channel within the required time. The time allotted to this operation may have been a portion of a longer timeout.". There's no inner exception.

The big problem is that the client application freezes when the main application process is started after one client has been disposed and a new one created. I've also noticed that when you close the WPF application, it doesn't close properly and keeps running in the background, preveting you from starting a new instance.