uploadSucceeded method of Upload button is being triggered twice instead on

[SHIRANSARUSI (SHIRANSARUSI Empty)]

vaadin version: 7, Why is uploadSucceeded triggered twice when uploading a file in vaadin 7 and how can I avoid it?

	upload.addSucceededListener(new Upload.SucceededListener() 
	{

		@Override
		public void uploadSucceeded(SucceededEvent event)
	   {
			  // XXX does something
	   }
	});