1. Run the test below on Linux.
2. drag the mouse from horizontal scrollbar into the scrollpane.
3. NPE thrown (this is different from Motif behaviour):
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: scrollpane child is null
        at sun.awt.X11.XScrollPanePeer.scroll(XScrollPanePeer.java:295)
        at sun.awt.X11.XScrollPanePeer.notifyValue(XScrollPanePeer.java:523)
        at sun.awt.X11.XScrollbar$1.run(XScrollbar.java:94)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:209)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:597)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:273)
        at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:183)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:173)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:168)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:160)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:121)

import java.awt.*;

public class Test extends Frame
{
    ScrollPane pane;

    public Test()
    {
        super("a test");
        pane = new ScrollPane(ScrollPane.SCROLLBARS_ALWAYS);
        add(pane, BorderLayout.CENTER);
    }

    public static void main (String str[])
    {
        Test f = new Test();
        f.setVisible(true);
        f.validate();
    }
}// class