C#: My callback function gets called twice for every Sent Request

I've Got a program that uploads/downloads files into an online server,Has a callback to report progress and log it into a textfile, The program is built with the following structure:

public void Upload(string source, string destination)
{     
        //Object containing Source and destination to pass to the threaded function
        KeyValuePair<string, string> file = new KeyValuePair<string, string>(source, destination);
       //Threading to make sure no blocking happens after calling upload Function
        Thread t = new Thread开发者_如何学Python(new ParameterizedThreadStart(amazonHandler.TUpload));
        t.Start(file);
}

  private void TUpload(object fileInfo)
{
    KeyValuePair<string, string> file = (KeyValuePair<string, string>)fileInfo;
    /*
    Some Magic goes here,Checking The file and Authorizing Upload
    */
    var ftiObject = new FtiObject () 
        { FileNameOnHDD = file.Key,
            DestinationPath = file.Value,
            //Has more data used for calculations.
        };
          //Threading to make sure progress gets callback gets called.
        Thread t = new Thread(new ParameterizedThreadStart(amazonHandler.UploadOP));
            t.Start(ftiObject);
            //Signal used to stop progress untill uploadCompleted is called.
            uploadChunkDoneSignal.WaitOne();
         /*
          Some Extra Code
         */
}

 private void UploadOP(object ftiSentObject)
{
  FtiObject ftiObject = (FtiObject)ftiSentObject;
  /* 
   Some useless code to create the uri and prepare the ftiObject.
  */  

   // webClient.UploadFileAsync will open a thread that 
   // will upload the file and report
   // progress/complete using registered callback functions.

  webClient.UploadFileAsync(uri, "PUT", ftiObject.FileNameOnHDD, ftiObject);
}

I got a callback that is registered to the Webclient's UploadProgressChanged event , however it is getting called twice per sent request.

 void UploadProgressCallback(object sender, UploadProgressChangedEventArgs e)
    {
        FtiObject ftiObject = (FtiObject )e.UserState;
                Logger.log(ftiObject.FileNameOnHDD, (double)e.BytesSent ,e.TotalBytesToSend);
    }

Log Output:

  Filename: C:\Text1.txt  Uploaded:1024 TotalFileSize: 665241
  Filename: C:\Text1.txt  Uploaded:1024 TotalFileSize: 665241
  Filename: C:\Text1.txt  Uploaded:2048 TotalFileSize: 665241
  Filename: C:\Text1.txt  Uploaded:2048 TotalFileSize: 665241
  Filename: C:\Text1.txt  Uploaded:3072 TotalFileSize: 665241
  Filename: C:\Text1.txt  Uploaded:3072 TotalFileSize: 665241
  Etc...

I am watching the Network Traffic using a watcher, and only 1 request is being sent.

Some how i cant Figure out why the callback is being called twice, my doubt was that the callback is getting fired by each thread opened(the main Upload , and TUpload), however i dont know how to test if thats the cause.

Note: The reason behind the many /**/ Comments is to indicate that the functions do more than just opening threads, and threading is being used to make sure no blocking occurs (there a couple of "Signal.WaitOne()" around the code for synchronization)

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If you put a breakpoint on the callback, can’t you check the callstack to see where the call came from? If you use Visual Studio that is.

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Have you checked that the API doesn't indeed call back twise with different info in UploadProgressChangedEventArgs?