WCF ConcurrencyMode Single and InstanceContextMode PerCall

I have an issue with my wcf service config. I would like every call to my service create a new instance of the service. For the concurrency I would like to one call is finished before another start.

Thus if I have a service like this one:

[ServiceBehavior(ConcurrencyMode=ConcurrencyMode.Single,
InstanceContextMode=InstanceContextMode.PerCall)]
public class MyService: IMyService
{
    public bool MyServiceOp()
    {
        Debug.WriteLine("thread "+ 
            Thread.CurrentThread.ManagedThreadId.ToString());
        Debug.WriteLine("start operation ");
        Do_work()
        Debug.WriteLine("end operation");
        return true;
    }
}

When I call it with multiple call in a loop, the trace give:

thread 1
thread 2
start operation
start operation
end operation
end operation

While I would like to have this:

thread 1 start operation end operation
thread 2 start operation end operation

Is this possible? Thank you