To reproduce: please refer to the attached gif file and sample project.

Workaround:

public class CustomNavigator : RadBindingNavigator
{
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadBindingNavigator).FullName;
        }
    }
    protected override RadBindingNavigatorElement CreateNavigatorElement()
    {
        return new CustomNavigatorElement();
    }
}

public class CustomNavigatorElement : RadBindingNavigatorElement
{
    public void Attach()
    {
        this.AttachEvents();
    }
}

private void radButton2_Click(object sender, EventArgs e)
{
    SetNavigator(list1, this.radGridView1);
    this.radGridView1.DataSource = list1;
    SetNavigator(list2, this.radGridView2);
    ((CustomNavigatorElement)this.radBindingNavigator1.BindingNavigatorElement).Attach();
}