In my current project, we're using ExtJS for almost all of the user interface. Our basic setup is a viewport with a border layout. In the center region of the layout, we launch the various components of the web application as new tabs.

When the contents of these tabs utilized a border layout, we began to notice a problem in IE6. When we loaded the viewport and launched multiple tabs (some using border layout) via onclick listeners,  those with border layout would lose their north and south regions when you toggled around between the tabs.

I looked at how the show/hide of tabs was working via Firebug and got a sneaky suspicion that the culprit was "display:none" being used to hide divs when you toggle tabs. After some exploration into ExtJS's RSS Feed Viewer example, we saw the property "hideMode:'offsets' ". We gave it a try and set it on the panels using border layout. This configuration tells Ext to hide the panel by using top and left positions of -1000 instead of "display:none" when the tab is hidden.