FeedbackPanel not clear

[Casper Kent]

I am trying to implement a "Clear" button on a form that will clear the
input fields as well as any feedback messages.  The fields are clear with
form.clearInput() but the feedback messages are not.  This is done with a
AjaxButton.  I thought when the feedback panel is added to the target, it
will make the messages disappeared but it does not.  Here is the relevant
code:

       form.add(new AjaxButton("clearButton") {
                @Override
                protected void onSubmit(AjaxRequestTarget target) {
                    form.clearInput();
                    target.add(form);
                    target.add(feedback);
                }
                @Override
                protected void onError(AjaxRequestTarget target) {
                    form.clearInput();
                    target.add(form);
                    target.add(feedback);
                }
            });