Bug 134856 [DataBinding] ValueDiff overrides Object.equals(Object) but not Object.hashCode()
The javadoc for Object.hashCode() states: "If two objects are equal according to the <tt>equals(Object)</tt> method, then calling the <code>hashCode</code> method on each of the two objects must produce the same integer result." The other IDiff implementations don't override Object.equals(Object) so I assume ValueDiff shouldn't either.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/observable/value/ValueDiff.java
/**
	 * @return the new value
	 */
	public abstract Object getNewValue();
	public boolean equals(Object obj) {
		if (obj instanceof ValueDiff) {
			ValueDiff val = (ValueDiff) obj;
			return Diffs.equals(val.getNewValue(), getNewValue())
					&& Diffs.equals(val.getOldValue(), getOldValue());
		}
		return false;
	}
	
	/**
	 * @see java.lang.Object#toString()
	 */
	public String toString() {
		StringBuffer buffer = new StringBuffer();
		buffer
			.append(getClass().getName())
			.append("{oldValue [") 
			.append(getOldValue() != null ? getOldValue().toString() : "null") 
			.append("], newValue [") 
			.append(getNewValue() != null ? getNewValue().toString() : "null") 
			.append("]}"); 
		
		return buffer.toString();
	}
}