HandlerRegistration.removeHandler() is NOT WORKING

[Tristan]

Hello,
I am stuck with the fact that HandlerRegistration.removeHandler() is
not removing my handler.
I have two controllers, say ParentController and ChildController,
each
implements ValueChangeHandler<String> to handle history events
The root class extended by both parent and child controllers:
public abstract class RootController implements
ValueChangeHandler<String>{
protected Controller parent = null;
protected HandlerRegistration historyHandler = null;
protected HashMap<String, Controller> childControllers = new
HashMap<String, Controller>(4);
public RootController(Controller parent){
this.parent = parent;
}
public giveHistoryControlTo(RootController controller){
historyHandler.removeHandler();
controller.setHistoryHandler( History.addValueChangeHandler
(controller));
History.fireCurrentHistoryState();
}
}

public class ParentController extends RootController implements Entry
Point {
public void onModuleLoad() {
childControllers.put( ChildController.NAME, new ChildController
(this));
historyHandler = History.addValueChangeHandler(this);
History.fireCurrentHistoryState():
}
.... at some point ParentController executes:
giveHistoryControlTo( childController.get
(ChildController.NAME));
**** the above works fine, handler is removed and new event is
**** handled by the child controller
}

public class ChildController extends RootController{
public ChildController(ParentController parent){
super(parent);
}
.... at some point ChildController executes:
giveHistoryControlTo( (ParentController) parent );
**** the above fails!!!
**** it appears as though handler is not removed as the
**** History.fireCurrentHistoryState() inside
giveHistoryControlTo
()
**** is being handled by the ChildController, instead of parent :
(
}

Feels like a bug. Is there a reason why .removeHandler() would not
immediately
do what it is supposed to?

- Tristan

ps.

"God helps those who help themselves"
I hacked a workaround. But the bug still remains.
(workaround was setting historyHandler to null when
giving up control and then explicitly calling the
parent's onValueChange() if historyHandler == null)