FULL PRODUCT VERSION :
java version "1.5.0_04"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_04-b05)
Java HotSpot(TM) Client VM (build 1.5.0_04-b05, mixed mode)

still repeatable with

java version "1.6.0-ea"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.6.0-ea-b51)
Java HotSpot(TM) Client VM (build 1.6.0-ea-b51, mixed mode, sharing)


ADDITIONAL OS VERSION INFORMATION :
Originally noticed in an application running on Windows 2000. Not reproduced on Linux, but the condensed test I wrote for this bug report also fails on Linux.

Linux bertha 2.6.12-1-686-smp #1 SMP Tue Aug 16 22:19:38 UTC 2005 i686 GNU/Linux
Windows XP

A DESCRIPTION OF THE PROBLEM :
i'm not sure what the real problem is here. that in the actual application, when run on Linux, the display is updated (possibly because of a setJMenuBar)? that setContentPane doesn't imply a need to re-validate? that the documentation doesn't mention this?

at least one of these things should change. personally, i'd favor having setContentPane do the right thing and cause re-validation.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. save the executable test case to Bug.java
2. javac Bug.java && java Bug

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
a window should appear with a JLabel; after a second, it should be replaced by a JTextArea.
ACTUAL -
the JLabel remains visible until the window is resized.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Bug extends JFrame {
 Bug() {
  setSize(new Dimension(640, 480));
  setContentPane(new JLabel("Hang on..."));
  setVisible(true);
  new Timer(1000, new ActionListener() {
   public void actionPerformed(ActionEvent e) {
    setContentPane(new JTextArea("Hello, World!"));
    // validate();
   }
  }).start();
 }
 public static void main(String[] args) {
  new Bug();
 }
}

---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
uncomment the call to validate.