Callback is not invoked on the client - wcf

Question

I have a self-hosted service that processes long running jobs submitted by a client over net.tcp binding. While the job is running (within a Task), the service will push status updates to the client via a one-way callback. This works fine, however when I attempt to invoke another callback to notify the client the job has completed (also one-way), the callback is never received/invoked on the client. I do not receive any exceptions in this process.
My Callback contract looks like this:
public interface IWorkflowCallback
{
[OperationContract(IsOneWay = true)]
[ApplySharedTypeResolverAttribute]
void UpdateStatus(WorkflowJobStatusUpdate StatusUpdate);
[OperationContract(IsOneWay = true)]
[ApplySharedTypeResolverAttribute]
void NotifyJobCompleted(WorkflowJobCompletionNotice Notice);
}
Code from the service that invokes the callbacks: (not in the service implementation itself, but called directly from the service implementation)
public WorkflowJobTicket AddToQueue(WorkflowJobRequest Request)
{
if (this.workflowEngine.WorkerPoolFull)
{
throw new QueueFullException();
}
var user = ServiceUserManager.CurrentUser;
var context = OperationContext.Current;
var workerId = this.workflowEngine.RunWorkflowJob(user, Request, new Object[]{new DialogServiceExtension(context)});
var workerjob = this.workflowEngine.FindJob(workerId);
var ticket = new WorkflowJobTicket()
{
JobRequestId = Request.JobRequestId,
JobTicketId = workerId
};
user.RegisterTicket<IWorkflowCallback>(ticket);
workerjob.WorkflowJobCompleted += this.NotifyJobComplete;
workerjob.Status.PropertyChanged += this.NotifyJobStatusUpdate;
this.notifyQueueChanged();
return ticket;
}
protected void NotifyJobStatusUpdate(object sender, PropertyChangedEventArgs e)
{
var user = ServiceUserManager.GetInstance().GetUserWithTicket((sender as WorkflowJobStatus).JobId);
Action<IWorkflowCallback> action = (callback) =>
{
ICommunicationObject communicationCallback = (ICommunicationObject)callback;
if (communicationCallback.State == CommunicationState.Opened)
{
try
{
var updates = (sender as WorkflowJobStatus).GetUpdates();
callback.UpdateStatus(updates);
}
catch (Exception)
{
communicationCallback.Abort();
}
}
};
user.Invoke<IWorkflowCallback>(action);
}
protected void NotifyJobComplete(WorkflowJob job, EventArgs e)
{
var user = ServiceUserManager.GetInstance().GetUserWithTicket(job.JobId);
Action<IWorkflowCallback> action = (callback) =>
{
ICommunicationObject communicationCallback = (ICommunicationObject)callback;
if (communicationCallback.State == CommunicationState.Opened)
{
try
{
var notice = new WorkflowJobCompletionNotice()
{
Ticket = user.GetTicket(job.JobId),
RuntimeOptions = job.RuntimeOptions
};
callback.NotifyJobCompleted(notice);
}
catch (Exception)
{
communicationCallback.Abort();
}
}
};
user.Invoke<IWorkflowCallback>(action);
}
In the user.Invoke<IWorkflowCallback>(action) method, the Action is passed an instance of the callback channel via OperationContext.GetCallbackChannel<IWorkflowCallback>().
I can see that the task that invokes the job completion notice is executed by the the service, yet I do not receive the call on the client end. Further, the update callback is able to be invoked successfully after a completion notice is sent, so it does not appear that the channel is quietly faulting.
Any idea why, out of these two callbacks that are implemented almost identically, only one works?
Thanks in advance for any insight.