HttpModule for processing static files with cassini

Question

public class MyModule : IHttpModule
{
    public void Dispose()
    {
     throw new NotImplementedException();
    }

    public void Init(HttpApplication context)
    {
     context.PostRequestHandlerExecute += delegate(object sender, EventArgs e)
     {
      System.Diagnostics.Trace.WriteLine("hello");
     };
    }
}

I see new "hello" line in my trace window everytime I request a same controller action. But if I request same static file multiple times it's traced only once and not anymore. I tested with Fiddler so I think it's not browser cache problem. Is it cassini bug or am I doing something wrong?