IIS calls BeginRequest of HttpModule twice. Is it a bug?

Steps

1. Create empty clean ASP.NET Web App - "MyApp". Deselect all options.
2. Create HttpModule - "MyHttpModule" (by MSDN example):

using System; using System.Web;

public class MyHttpModule : IHttpModule { public MyHttpModule() { }

public string ModuleName { get { return "MyHttpModule"; } }
public void Dispose() { }

public void Init(HttpApplication app)
{
    app.BeginRequest += ProcessBeginRequest;
}

private void ProcessBeginRequest(object source, EventArgs e)
{
    var ctx = ((HttpApplication)source).Context;

    if (ctx.Request.Path == "/favicon.ico") { return; } // This stuff is handled automatically in current IIS version. So, I wrote this line just in case.

    ctx.Response.Write("Processing request from: " + ctx.Request.Url + "<br />");
    ctx.Response.Flush();
}

}

3. Include it to web.config:

   <system.webServer> <modules> <add name="MyHttpModule" type="MyHttpModule, MyApp"/> </modules> </system.webServer>

4. Run the app

5. Browser shows that BeginRequest listener was triggered twice for single http reques:

Attempts

1. LogRequest event listener is executed as expected. But this is not proper name listener for http processing work

2. Changes like this one had no result:

   app.BeginRequest -= ProcessBeginRequest;
   app.BeginRequest += ProcessBeginRequest;
   
   

3. Not a favicon.ico thing

Question

Why event handler of single http request was called twice?

How risky it is to start any low-level http request processing with IIS? (that is something more than just logging)

PS: After surfing the internet I'm thinking this is IIS bug. Am I wrong? Of course, for low-level processing of http requests and for maximum performance it's better to self-host the application or use some prepared set of components for self-hosting like Katana. But I wonder if IIS be extended with such stuff safely? Cause I have a bad feeling about it, as now it tells to me stay out of http level, do nothing more than logging there and use IIS configuration only.