FULL PRODUCT VERSION :
java version "1.6.0_14"
Java(TM) SE Runtime Environment (build 1.6.0_14-b08)
Java HotSpot(TM) Client VM (build 14.0-b16, mixed mode)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

A DESCRIPTION OF THE PROBLEM :
Upgrading to this release has caused the following code to fail:

        Exception cause = new Exception();
        SAXException e = new SAXException("A SAX exception");
        e.initCause(cause);
        System.out.println(cause == e.getCause());

Using 6u14 this now prints "false" because initCause(Throwable t); is not overriden in SAXException.

Taking a step back though, why do you need to store the Exception in SAXException? Why can you not simply delegate all calls to Throwable? I see no logic that SAXException adds on top of Throwable, it just provides a getException() method.

It seems it last worked under:

Java version "1.6.0_13"
Java(TM) SE Runtime Environment (build 1.6.0_13-b03)
Java HotSpot(TM) Client VM (build 11.3-b02, mixed mode)

I've also tried a few other earlier ones (1.6.0_11, 1.6.0_06, 1.5.0_17)

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
        Exception cause = new Exception();
        SAXException e = new SAXException("A SAX exception");
        e.initCause(cause);
        System.out.println(cause == e.getCause());

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Should output: "true"
ACTUAL -
outputs "false"

REPRODUCIBILITY :
This bug can be reproduced always.

---------- BEGIN SOURCE ----------
import org.xml.sax.SAXException;


public class Test {

     public static void main(String[] args) {
        Exception cause = new Exception();
        SAXException e = new SAXException("A SAX exception");
        e.initCause(cause);
        System.out.println(cause == e.getCause());
    }

}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Do not use the initCause();

Release Regression From : 6u13
The above release value was the last known release where this 
bug was not reproducible. Since then there has been a regression.