google maps kml layer refresh problem

I have a kml layer on my google maps app. I tried to refresh the kml layer by generating a new google.maps.KmlLayer object every 10s. The kml file contains customized icons. It works fine for the first several times of refreshing. However after a few minutes, the kml layer disappears (the icons disappear but they are still clickable). Any ideas why the kml layer disappears?

Here is the snippet of my code:

function initialize() {
        var p = new google.maps.LatLng(36.668419,-119.267578);
        var mapOptions = {
          zoom: 5,
          center: p,
          mapTypeId: google.maps.MapTypeId.ROADMAP
        };
        map = new google.maps.Map(document.getElementById("map_canvas"),
            mapOptions);

        var kmllayer = new google.maps.KmlLayer('http://api.flickr.com/services/feeds/geo/?g=322338@N20&lang=en-us&format=feed-georss'
          + '?key='
          + Math.ra开发者_JAVA技巧ndom(),
          ({'preserveViewport': true}));
        geotaggingLayer.setMap(map);

        setInterval(refresh, 10000, kmllayer);
      }

      function refresh(layer) {

          var newkmllayer = new google.maps.KmlLayer('http://api.flickr.com/services/feeds/geo/?g=322338@N20&lang=en-us&format=feed-georss'
            + '?key='
            + Math.random(),
            ({'preserveViewport': true}));
          layer.setMap(null);
          newkmllayer.setMap(map);
      }

Thank you.