below is a simplified sample to explain the issue.
Viewport west region containing a panel whose 'contentEl' contains an '<object>' tag( eg. a youtube video embedding).

On collaspse/expand the region in Internet explorer is flickering the whole UI. Looks like everything is refreshed and rendered again in the page.

The behaviour is proper in chrome.

Code:
Ext.onReady(function () {

    var west = new Ext.Panel({
        region: 'west',
        margins: '5 0 5 5',
        split: true,
        width: 350,
        collapsible: true,
        contentEl: 'westContent'
    });

    var viewport = new Ext.Viewport({
        layout: 'border',
        items: [
        west, {
            region: 'center',
            margins: '5 5 5 0',
            cls: 'empty',
            bodyStyle: 'background:#f1f1f1',
            html: '<br/><br/>&lt;empty center panel&gt;'
        }]
    });
});
<div id='westContent'>
<object type="application/x-shockwave-flash" width="425" height="350" data="http://www.youtube.com/v/HvfNl-kkqYs"><param name="movie" value="http://www.youtube.com/v/HvfNl-kkqYs" /></object>
</div>