Ninject with Owin: InRequestScope doesn't work

Question

I created a project with EF6 + Ninject + Owin. I realized that Ninject InRequestScope doesn't work, infact, in a single Web Api request the constructor of my DBContext derived class fires more than once.

The Startup file of my web api project is like:

public void Configuration(IAppBuilder app)
{
    ConfigureOAuth(app);
    HttpConfiguration config = new HttpConfiguration();
    WebApiConfig.Register(config);
    app.UseWebApi(config);

    app.UseNinjectMiddleware(CreateKernel).UseNinjectWebApi(config);
}

private static IKernel CreateKernel()
{
    // I have my Ninject module in a separate assembly
    var kernel = new StandardKernel(new Core.Ioc.AutoBotMapper());

    GlobalConfiguration.Configuration.DependencyResolver = new NinjectDependencyResolver(kernel);

    return kernel;
}

My Module:

public class AutoBotMapper : NinjectModule
{
    private readonly ILog _logger = LogManager.GetLogger("CORE");

    public override void Load()
    {
        // Contesto is my DBContext
        Bind<Contesto>().ToSelf().InRequestScope(); 

        // Other Binds
        Bind<ITournamentServiceFactory>().ToFactory();
        Bind<ITournamentCloser>().To<TournamentCloser>();

        ...
    }
}

I don't use the Bootstrapper "NinjectWebCommon" since i found this approach on the net.

Does exist a way to bypass this bug?