How to reproduce: add several menu items displaying only images to the split button and set the MaximumSize property of the drop-down menu

Workaround:
public RadForm1()
{
    InitializeComponent();

    this.radSplitButton1.DropDownButtonElement.DropDownMenu.MaximumSize = new Size(30, 0);
    RadScrollBarElement element = this.radSplitButton1.DropDownButtonElement.DropDownMenu.PopupElement.FindDescendant<RadScrollBarElement>();
    element.Visibility = Telerik.WinControls.ElementVisibility.Collapsed;
    element.RadPropertyChanging += Element_RadPropertyChanging;
}

private void Element_RadPropertyChanging(object sender, Telerik.WinControls.RadPropertyChangingEventArgs args)
{
    if (args.Property.Name == "Visibility")
    {
        args.Cancel = true;
    }
}