A DESCRIPTION OF THE REGRESSION :
The JTable header no longer supports ComponentOrientation.RIGHT_TO_LEFT. For some applications it is preferred to have the column header icon to appear on the right of the header text. This is done creating a proxy cell renderer that installs a custom icon and force the component orientation of cell renderer component.

REPRODUCIBLE TESTCASE OR STEPS TO REPRODUCE:
import java.awt.*;
import javax.swing.*;
import javax.swing.table.*;

public class IconTest implements Runnable {
  
  public void run() {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JTable table = new JTable(new NumberModel());
    table.getTableHeader().setDefaultRenderer(
            new HeaderRenderer(table.getTableHeader().getDefaultRenderer()));
    frame.getContentPane().add(new JScrollPane(table));
    frame.setSize(640, 480);
    frame.validate();
    frame.setVisible(true);
  }
  
  private static class HeaderRenderer implements TableCellRenderer, Icon {
    private final TableCellRenderer defaultRenderer;
    
    private HeaderRenderer(TableCellRenderer d) {
      assert d != null;
      this.defaultRenderer = d;
    }
    
    public Component getTableCellRendererComponent(JTable table, Object value,
                          boolean isSelected, boolean hasFocus, int row, int column) {
      JLabel comp = (JLabel)defaultRenderer.
              getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);
      final JTableHeader header = table.getTableHeader();
      if(header != null) {
        comp.setForeground(header.getForeground());
        comp.setBackground(header.getBackground());
        comp.setFont(header.getFont());
      }
      else {
        comp.setText("Null header");
      }
      comp.setBorder(UIManager.getBorder("TableHeader.cellBorder"));
      comp.setHorizontalAlignment(SwingConstants.CENTER);
      
      
      comp.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);
      comp.setIcon(this);
      return comp;
    }
    
     public int getIconWidth() {return 7;}
     public int getIconHeight() {return 7;}

     /**
      * Paints a triangle on the table header.
      * @param comp the component.
      * @param g the graphics used to paint.
      * @param x the origin x
      * @param y the origin y
      */
     public void paintIcon(Component comp, Graphics g, int x, int y) {
       final int height = getIconHeight();
       final int width = getIconWidth();
       final Color c = comp.getBackground();

       Color brighter = c.brighter();
       Color darker = c.darker();

       g.setColor(darker);
       g.drawLine(x, y, x + width / 2, y + height); //left side
       g.setColor(brighter);
       g.drawLine(x, y, x + width, y); //top
       g.drawLine(x + width, y, x + width / 2, y + height); //right side
       g.setColor(c);
     }
  }
  
  private static class NumberModel extends AbstractTableModel {
    public int getRowCount() {return 7;}
    public int getColumnCount() {return 7;}
    public Object getValueAt(int row, int col) {
      return Integer.valueOf(row * this.getColumnCount() + col);
    }
  }
  
  public static void main(String[] args) {
    SwingUtilities.invokeLater(new IconTest());
  }
}

RELEASE LAST WORKED:
5.0 Update 6

RELEASE TEST FAILS:
mustang-b70

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The icon for each column header should appear on the right side of the text.
ACTUAL -
The icon always appears on left of the header text.

OBSERVED APPLICATION IMPACT:
Icon is on the wrong side.