WCF callback generated interface

Question

.NET Framework 3.5. On the server side I have an interface

public interface IClientCallback
{
    [OperationContract(IsOneWay = true)]
    void ReceiveBroadcast(string nickname, string message);

    [OperationContract(IsOneWay = true)]
    void ReceivePrivate(string nickname, string message);

    [OperationContract(IsOneWay = true)]
    void UserJoined(string nickname);

    [OperationContract(IsOneWay = true)]
    void UserLeft(string nickname);
}

with svcutil I've got the folliwing interface generated

public interface IServerCallback
{

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, Action="http://tempuri.org/IServer/ReceiveBroadcast")]
    void ReceiveBroadcast(string nickname, string message);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, AsyncPattern=true, Action="http://tempuri.org/IServer/ReceiveBroadcast")]
    System.IAsyncResult BeginReceiveBroadcast(string nickname, string message, System.AsyncCallback callback, object asyncState);

    void EndReceiveBroadcast(System.IAsyncResult result);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, Action="http://tempuri.org/IServer/ReceivePrivate")]
    void ReceivePrivate(string nickname, string message);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, AsyncPattern=true, Action="http://tempuri.org/IServer/ReceivePrivate")]
    System.IAsyncResult BeginReceivePrivate(string nickname, string message, System.AsyncCallback callback, object asyncState);

    void EndReceivePrivate(System.IAsyncResult result);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, Action="http://tempuri.org/IServer/UserJoined")]
    void UserJoined(string nickname);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, AsyncPattern=true, Action="http://tempuri.org/IServer/UserJoined")]
    System.IAsyncResult BeginUserJoined(string nickname, System.AsyncCallback callback, object asyncState);

    void EndUserJoined(System.IAsyncResult result);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, Action="http://tempuri.org/IServer/UserLeft")]
    void UserLeft(string nickname);

    [System.ServiceModel.OperationContractAttribute(IsOneWay=true, AsyncPattern=true, Action="http://tempuri.org/IServer/UserLeft")]
    System.IAsyncResult BeginUserLeft(string nickname, System.AsyncCallback callback, object asyncState);

    void EndUserLeft(System.IAsyncResult result);
}

As you see it provides End* and Begin* methods though all the operations are one way. What could be the cause? I tried adding AsyncPattern = false to IClientCallback methods, but without result.