Switch the swingset to Windows or Organic.
Switch to InternalFrame
Check all the checkboxs and create a frame
Now click near the edge of one of the titlepane buttons while dragging.
Do this several times. It will eventually hork!

java.lang.NullPointerException
        at com.sun.java.swing.basic.BasicInternalFrameUI$BorderListener.mouseDragged(BasicInternalFrameUI.java:586)
        at java.awt.Component.processMouseMotionEvent(Component.java:2327)
        at com.sun.java.swing.JComponent.processMouseMotionEvent(JComponent.java:1479)
        at java.awt.Component.processEvent(Component.java:2133)
        at java.awt.Container.processEvent(Container.java:894)
        at java.awt.Component.dispatchEventImpl(Component.java:1764)
        at java.awt.Container.dispatchEventImpl(Container.java:939)
        at java.awt.Component.dispatchEvent(Component.java:1704)
        at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:1548)
        at java.awt.LightweightDispatcher.processMouseEvent(Container.java:1449)
        at java.awt.LightweightDispatcher.dispatchEvent(Container.java:1392)
        at java.awt.Container.dispatchEventImpl(Container.java:926)
        at java.awt.Window.dispatchEventImpl(Window.java:443)
        at java.awt.Component.dispatchEvent(Component.java:1704)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:63)