JScrollPane doesn't update scrollbar when window is maximized

Question

In my GUI, I have a JSplitPane containing two JTextArea controls enclosed in a JScrollPane, all enclosed in a JFrame.

I am having problems with the scrollbar updating when the window is maximized. The scrollbar updates correctly when the window is minimized, but fails to appear when I try to create a new line in one of the text areas. It updates when I minimize the window, but I am trying to get the scroll bar to update when the window is maximized.

        this.text = new JTextArea(15, 70);

        this.text.getDocument().addDocumentListener(this);
        this.text.setBorder(BorderFactory.createLineBorder(Color.BLACK));
        this.text.setLineWrap(true);

        //Create lines
        JTextArea lines = new JTextArea(15, 2);
        lines.setBorder(BorderFactory.createLineBorder(Color.BLACK));

        int lineHeight = lines.getRows();
        int i = 1;
        while (i <= lineHeight + 1) {
            lines.append(Integer.toString(i) + "\n");
            i++;
        }
        lines.setEditable(false);

        //Pack it all

        JSplitPane combo = new JSplitPane(JSplitPane.HORIZONTAL_SPLIT, lines,
                this.text);
        combo.setResizeWeight(0d / 10d);

        //Create scrolling area

        JScrollPane scroller = new JScrollPane(combo);
        scroller.setVerticalScrollBarPolicy(
                ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

I have some more code regarding a menu and putting everything into a frame if that is important. I believe I am using the default layout manager.