Wicket feedback message and AjaxButton

I have a form containing just a TextField and a Button. I notice that if I set the text field as required and click on the button, I get the appropriate feedback message.

However, when I have an AjaxButton instead (which is what I need, because I need to execute a callback method with an AjaxRequestTarget), I do not see the feedback message, unless I reload. Upon debugging, I noticed that the onSubmit method of the form is called (the onError too), but the onSubmit method of the AjaxButton is not.

What do you suggest I do so that I can see the feedback message and call a callback method?

        Form<Void> form = new Form<>("form");

        // added the textfield too

        form.add(new AjaxButton("startButton") {
            private static final long serialVersionUID = 1L;

            protected void onSubmit(AjaxRequestTarget target, Form<?> form) {
                // some action
                target.add(this);
            }

        });
        add(form);

        <form wicket:id="form">
            <table>
                <tbody>
                    <tr>
                        <!-- some stuff -->
                    </tr>
                    <tr>
                        <td><input type="submit" wicket:id="startButton" class="roundedButton"></input></td>
                    </tr>
                </tbody>
            </table>
        </form>

I can't see your entire code but you might need to add the FeedbackPanel to AjaxRequestTarget when onError is triggered.