Why doesn't extjs qtip on combobox show up in internet explorer ?

Question

hi all,

I've added an extJS quicktip (qtip) to an extJS combobox and it works well in FF, Chrome, Safari but not in IE7 and IE8.

Here is a code snippet:

 var searchConfig = {
        store: store,
        tpl: tpl,
        hideTrigger: false,
        minChars: 1,
        queryDelay: 50,
        emptyText: OpenLayers.i18n('Geo search...'),
        loadingText: OpenLayers.i18n('loadingText'),
        displayField: 'label',
        cls: 'cbSearchCls',
        ctCls: 'cbSearchContainerCls',
        width: config.width || 200,
        listWidth: 280,
        selectOnFocus: true,
        triggerClass: 'loupe',
        listeners:{
            'render':function() {
            this.el.set(
                {qtip: OpenLayers.i18n('searchQuicktip'),
                 qwidth: 400
                 }
                );
                this.validate();
            }
        }
    };
    if (config.renderTo) {
        searchConfig['renderTo'] = config.renderTo;
    }
    var search = new Ext.form.ComboBox(searchConfig);

    //configure quicktip shown on search box
    Ext.apply(Ext.QuickTips.getQuickTip(), {
        showDelay: 50,      // Show 50ms after entering target
        dismissDelay: 10000,
        trackMouse: true

    });

The application can be viewed online under http://map.geoportal.lu?lang=en When you move your mouse over the search box on the top, you'll see a quicktip appear. In IE, nothing happens.

What am I missing?

Kind regards

jay