This is our test.zul file. It opens with with version 6.0.0 and 6.0.1. With version 6.02 and 6.5 this page hangs.
While using version 6.0.2 i found the following dependency:
It opens if I use Open Street Map instead of Google map. But if I keep on adding simple controls like buttons, lists, tabs and so on I reach a point where adding a single button produces the same problem.
I can only guess I reach a certain javascript object count limit. But this is as far as my knowledge goes.

<zk>
<window width="100%" height="100%" apply="org.zkoss.bind.BindComposer" viewModel="@id('vm') @init('test.TestMapViewModel')">
<borderlayout>
<center>
<div id="map" style="border: 1px solid black; width: 1000px; height: 600px;"></div>
</center>
</borderlayout>
</window>
<script src="http://maps.google.com/maps/api/js?v=3.2&sensor=false"></script>
<script src="http://openlayers.org/api/2.11/OpenLayers.js"></script>
<script><![CDATA[

zk.afterMount(function()

{ init(); }

);

var Map;
var epsg4326 = new OpenLayers.Projection("EPSG:4326");

function init()
{
Map = new OpenLayers.Map({
controls: [
new OpenLayers.Control.Navigation(

{documentDrag: true}

)
],
div: zk.Widget.$("$map").uuid
});

var gmap = new OpenLayers.Layer.Google(
"Google Streets",

{numZoomLevels: 20}

);

Map.addLayers([gmap]);
Map.setBaseLayer(gmap);
Map.setCenter(new OpenLayers.LonLat(25, 43).transform(epsg4326, Map.getProjectionObject()), 7);
}

]]></script>
</zk>