Workaround: use bigger images
public partial class Form2 : RadForm
{
    public Form2()
    {
        InitializeComponent();
    }

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);

        this.radBindingNavigator1.BindingNavigatorElement.MovePreviousItemButtonImage = Image.FromFile("MovePreviousItemButtonImage.png");
        this.radBindingNavigator1.BindingNavigatorElement.MoveFirstItemButtonImage = Image.FromFile("MoveFirstItemButtonImage.png"); ;
        this.radBindingNavigator1.BindingNavigatorElement.MoveNextItemButtonImage = Image.FromFile("MoveNextItemButtonImage.png");
        this.radBindingNavigator1.BindingNavigatorElement.MoveLastItemButtonImage = Image.FromFile("MoveLastItemButtonImage.png");
        this.radBindingNavigator1.BindingNavigatorElement.AddNewButtonImage = Image.FromFile("AddNewButtonImage.png");
        this.radBindingNavigator1.BindingNavigatorElement.DeleteButtonImage = Image.FromFile("DeleteButtonImage.png");
    }
}