FULL PRODUCT VERSION :
java version "1.6.0_01"
Java(TM) SE Runtime Environment (build 1.6.0_01-b06)
Java HotSpot(TM) Client VM (build 1.6.0_01-b06, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Windows

A DESCRIPTION OF THE PROBLEM :
The font renderer in Java should ignore the three invisible characters (http://unicode.org/charts/PDF/U2000.pdf):

U+2061 FUNCTION APPLICATION
U+2062 INVISIBLE TIMES
U+2063 INVISIBLE SEPARATOR

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
javax.swing.JOptionPane.showMessageDialog( null, "a\u2063+\u2063a\u2063=\u20632\u2062a" );

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The chars \u2062 and \u2063 should give no visible glyph or a small space.
ACTUAL -
The ui shows boxes for an unknown character.

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
package com.tutego.bug.sun;

public class U2062a
{
  public static void main( String[] args )
  {
    String string = "a\u2063+\u2063a\u2063=\u20632\u2062a";
    
    javax.swing.JOptionPane.showMessageDialog( null, string );
  }
}

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

CUSTOMER SUBMITTED WORKAROUND :
Replace all INVISIBLE chars.

string = string.replaceAll( "\u2061|\u2062|\u2063", "" );