google 地图调用有时出现残缺现象

  <div>
<script src="scripts/jquery-1.2.3-intellisense.js" type="text/javascript"></script>
  <script src="scripts/jquery-1.3.2.min.js" type="text/javascript"></script>
    <script src="http://www.google.cn/maps?file=api&amp;v=2&amp;key=ABQIAAAAzr2EBOXUKnm_jVnk0OJI7xSosDVG8KKPE1-m51RBrvYughuyMxQ-i1QfUnH94QxWIa6N4U6MouMmBA&hl=zh-CN"
        type="text/javascript"></script>
          <script type="text/javascript">
    function initialize() {
      if (GBrowserIsCompatible()) {
        var map = new GMap2(document.getElementById("map_canvas"));
        map.setCenter(new GLatLng(39.917,116.397), 14);
        GEvent.addListener(map,"click", function(overlay,latlng) {     
          var myHtml = "GPoint 为： " + latlng.x+"&nbsp;&nbsp;&nbsp;&nbsp;"+latlng.y+ " <br>缩放级别为：" + map.getZoom();
 $("#txtLatitude").val(latlng.x);
 $("#txtLongitude").val(latlng.y);
 $("#txtZoom").val(map.getZoom());
          map.openInfoWindow(latlng, myHtml);
        });
        map.addControl(new GSmallMapControl());
        map.addControl(new GMapTypeControl());
      }
    }   
    </script>
<script src="JScript.js" type="text/javascript"></script>
<body onload="initialize()" onunload="GUnload()">
   经度： <input id="txtLongitude" type="text" />  纬度： <input id="txtLatitude" type="text" />  缩放系数： <input id="txtZoom" type="text" />
    <div id="map_canvas" style="width: 600px; height: 300px">
    </div>
    <input id="btnOk" type="button" value="button" />
    <div style="display: none">
        <input id="lat" type="text" />
        <input id="lng" type="text" />
        <input id="zoom" type="text" />
    </div>
    <input id="btnOutput" type="button" value="button" />
    
    </div>