AllowModificationWhileListening=true required for using interfaces with events?

[doxxx]

I'm trying to write a helper class for clients which encapsulates the code for making a JsonRPC connection over WebSocket to a service with a specific interface.

When using a service interface that contains an event, if I don't set AllowModificationWhileListening to true when I execute jsonRpc.Attach<TService>(), it throws an exception on the client side saying:

This cannot be done after listening has started.

Is this expected or am I doing something wrong?

Client helper:

class RpcServiceClient<TService> : IAsyncDisposable
    where TService : class
{
    private readonly ClientWebSocket _socket;
    private readonly JsonRpc _jsonRpc;
    private readonly TService _proxy;

    public static async Task<RpcServiceClient<TService>> ConnectAsync(string url, CancellationToken token)
    {
        var socket = new ClientWebSocket();
        await socket.ConnectAsync(new Uri(url), token).ConfigureAwait(false);

        try
        {
            var jsonRpc = new JsonRpc(new WebSocketMessageHandler(socket));
            jsonRpc.StartListening();
            //jsonRpc.AllowModificationWhileListening = true;
            var proxy = jsonRpc.Attach<TService>();
            //jsonRpc.AllowModificationWhileListening = false;
            return new RpcServiceClient<TService>(socket, jsonRpc, proxy);
        }
        catch
        {
            await socket.CloseAsync(WebSocketCloseStatus.ProtocolError, "JSON-RPC setup failed", CancellationToken.None).ConfigureAwait(false);
            throw;
        }
    }

    private RpcServiceClient(ClientWebSocket socket, JsonRpc jsonRpc, TService proxy)
    {
        _socket = socket;
        _jsonRpc = jsonRpc;
        _proxy = proxy;
    }

    public TService Service => _proxy;

    public async ValueTask DisposeAsync()
    {
        await _socket.CloseAsync(WebSocketCloseStatus.NormalClosure, "Client closing", CancellationToken.None).ConfigureAwait(false);
        _jsonRpc.Dispose();
    }
}

Example problematic interface:

public interface IBarService : IDisposable
{
    Task SumAsync(IEnumerable<int> values);

    event EventHandler<int> SumResult;
}