The following program shows the "pane" parameter passed into
JOptionPane.showOptionDialog is being painted twice!

import java.awt.*;
import com.sun.java.swing.*;

public class PaintTest extends JFrame
{
   public PaintTest()
   {
      JPanel pane = new JPanel(new BorderLayout());
      JPanel titlePanel = new JPanel(new BorderLayout());
      titlePanel.add(new JLabel("Title"), "Center");
      pane.add(titlePanel, "North");

      JScrollPane scrollFilterPane =
         new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
                         JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
      scrollFilterPane.setAlignmentX(JScrollPane.LEFT_ALIGNMENT);
      scrollFilterPane.setAlignmentY(JScrollPane.TOP_ALIGNMENT);

      JViewport vp = scrollFilterPane.getViewport();
      vp.add(new JPanel());
      pane.add(scrollFilterPane, "Center");

      JOptionPane.showOptionDialog(this, pane, "Title",
                                   JOptionPane.DEFAULT_OPTION,
                                   JOptionPane.PLAIN_MESSAGE, null,
                                   new Object[] {new JPanel()},
                                   null);
   }

   public static void main(String[] argv)
   {
      PaintTest dlg = new PaintTest
();
   }
}