Bug 158065 [DataBinding] ValidationError observables need a nudge to hook themselves up
See attached patch.
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/observable/value/ComputedValue.java
for (int i = 0; i < dependencies.length; i++) {
				IObservable observable = dependencies[i];
				observable.removeChangeListener(privateInterface);
				observable.removeStaleListener(privateInterface);
			}
			
			final Object oldValue = cachedValue;
			
			
			fireValueChange(new ValueDiff() {
				public Object getOldValue() {
					return oldValue;
				}
				public Object getNewValue() {
					return getValue();
				}
			});
		}
	}
	public boolean isStale() {
		
		getValue();
		return stale;
	}
	public Object getValueType() {
		return valueType;
	}
}