GWT: Class 'MenuItem' doesn't implement 'IsWidget' interface

I have strange code inspection errors on UiBinder xml file with MenuItem element

IDE marks all MenuItem elements in uibinder xml file "Class 'MenuItem' doesn't implement 'IsWidget' interface"

I've tryied to test on empty project created from scratch. The error still exists.

Using GWT 2.8.2

TestMenu.ui.xml:

<ui:UiBinder xmlns:ui='urn:ui:com.google.gwt.uibinder'
             xmlns:g='urn:import:com.google.gwt.user.client.ui'>
    <g:HTMLPanel>
        <g:MenuBar ui:field="menu">
            <g:MenuItem text="Menu1">
                <g:MenuBar vertical="true">
                    <g:MenuItem text="Menu2"/>
                </g:MenuBar>
            </g:MenuItem>
        </g:MenuBar>
    </g:HTMLPanel>
</ui:UiBinder>

TestMenu.java:

package com.mySampleApplication.client;

import com.google.gwt.core.client.GWT;
import com.google.gwt.uibinder.client.UiBinder;
import com.google.gwt.uibinder.client.UiField;
import com.google.gwt.user.client.ui.Composite;
import com.google.gwt.user.client.ui.HTMLPanel;
import com.google.gwt.user.client.ui.MenuBar;

public class TestMenu extends Composite {
    interface TestMenuUiBinder
            extends UiBinder<HTMLPanel, TestMenu> {
    }

    private static TestMenuUiBinder ourUiBinder = GWT.create(TestMenuUiBinder.class);

    @UiField MenuBar menu;

    public TestMenu() {
        initWidget(ourUiBinder.createAndBindUi(this));
    }
}

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