FULL PRODUCT VERSION :
java version "1.4.2"
java version "1.5.0"
java version "1.6.0_03"

ADDITIONAL OS VERSION INFORMATION :
Linux, Windows

A DESCRIPTION OF THE PROBLEM :
The getMaximumSize() method, applied to a JRootPane instance,
returns a width of 0. This is smaller than the width returned by
getMinimumSize() and by getPreferredSize() of the same instance.

For reference, the maximum size of a JPanel is [2147483647,2147483647]
(due to the BorderLayout).

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile and run this program:
================ bug.java =====================
import javax.swing.*;

public class bug {
  public static void main (String args[]) {
    JRootPane r = new JRootPane();
    r.getContentPane().add(new JLabel("foo"));
    System.out.println(r.getMinimumSize());
    System.out.println(r.getPreferredSize());
    System.out.println(r.getMaximumSize());
  }
}
===================================================

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
It should print:
java.awt.Dimension[width=21,height=15]
java.awt.Dimension[width=21,height=15]
java.awt.Dimension[width=2147483647,height=2147483647]

ACTUAL -
It prints:
java.awt.Dimension[width=21,height=15]
java.awt.Dimension[width=21,height=15]
java.awt.Dimension[width=0,height=2147483647]


REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import javax.swing.*;

public class bug {
  public static void main (String args[]) {
    JRootPane r = new JRootPane();
    r.getContentPane().add(new JLabel("foo"));
    System.out.println(r.getMinimumSize());
    System.out.println(r.getPreferredSize());
    System.out.println(r.getMaximumSize());
  }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Use the getContentPane().getMaximumSize() instead of getMaximumSize().