Version(s) of Ext GWT
Ext GWT 3.0 Release Candidate 2

Browser versions and OS (and desktop environment, if applicable)
IE 9, Windows 7

Virtual Machine
No

Description
First of all: you should mention somewhere that it is necessary to use a ContentPanel to make a BorderLayout-Panel collapsible. A simple BorderLayoutData.setCollapsible(true) doesn't do the thing. I'm not sure whether it's a bug or designed that way. But what actually seems to be a bug: BorderLayoutData.isCollapsed() always returns false (see code below). One workaround is to use BorderLayoutContainer.addCollapsedHandler() and set the collapsed state manually. The other way to get the state is to call the wrapped ContentPanel's isCollapsed(). Again - not the expected behaviour.

Run mode
Development Mode

Test case

Code:
 public void onModuleLoad()
    {
        BorderLayoutContainer blc = new BorderLayoutContainer();
        blc.setPixelSize(400, 200);

        TextButton button = new TextButton("Is Collapsed?");
        final Label label = new Label("Center");

        final BorderLayoutData bld = new BorderLayoutData(50);
        bld.setCollapsible(true);

        ContentPanel cp = new ContentPanel();
        cp.setCollapsible(true);
        cp.setWidget(new TextButton("dummy"));

        blc.setNorthWidget(button, new BorderLayoutData(30));
        blc.setWestWidget(cp, bld);
        blc.setCenterWidget(label);

        button.addSelectHandler(new SelectHandler()
        {
            @Override
            public void onSelect(SelectEvent event)
            {
                label.setText(bld.isCollapsed() ? "collapsed!" : "not collapsed!");
            }
        });

        RootPanel.get().add(blc);
    }