Problem with JTable and DefaultCellEditor

I have a JTable with editable columns, some of which should accept only
numbers. To do this, I have added a DefaultCellEditor to the numeric
columns, with a JTextField to accept user input, and a KeyListener to
filter out non-numeric keystrokes from the JTextField.

The user can start editing by mouse-clicking in a cell and typing, or
by navigating around the table using the arrow keys, then type in a
cell, without using the mouse.

All this works well, except in the second case when the user types in a
cell without first selecting it with the mouse. The problem here is
that the KeyListener does not see the first keystroke, but does see
subsequent ones. That means one non-numeric character can be entered
into the cell. However, the KeyListener always works if the user first
selects the cell with a mouse-click. Below is some code showing this
behaviour. What am I missing? How can I capture that first keystroke? I
am using Java 1.5.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.table.*;

public class Test extends JFrame {
  public Test() {
    JTable table = new JTable(new Object[][] { {"a",1,2},{"b",3,4} },
                              new String[] {"Text", "Num 1", "Num 2"});
    table.setRowSelectionAllowed(false);
    table.setSurrendersFocusOnKeystroke(true);

    TableColumnModel cm = table.getColumnModel();
    cm.getColumn(1).setCellEditor(new MyCellEditor());
    cm.getColumn(2).setCellEditor(new MyCellEditor());

    JScrollPane scrollPane = new JScrollPane(table);
    getContentPane().add(scrollPane);
  }

  private class MyCellEditor extends DefaultCellEditor {
    private final JTextField tf;

    public MyCellEditor() {
      super(new JTextField());
      tf = (JTextField) getComponent();
      tf.addKeyListener(new MyKeyListener ());
      setClickCountToStart(1);
    }

    public Component getTableCellEditorComponent(JTable table,
              Object value, boolean isSelected, int row, int column) {
      tf.setText(value.toString());
      return tf;
    }

    public Object getCellEditorValue() {
      return tf.getText();
    }
  }

  private class MyKeyListener implements KeyListener {
    public void keyPressed(KeyEvent e) {}
    public void keyReleased(KeyEvent e) {}
    public void keyTyped(KeyEvent e) {
      if ( ! Character.isDigit(e.getKeyChar()) ) {
        Toolkit.getDefaultToolkit().beep();
        e.consume();
      }
    }
  }

  public static void main(String[] args) {
    Test frame = new Test();
    frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

Mike