In lightweight the issue is not observed:

<telerik:RadRibbonBar runat="server" RenderMode="Classic">
    <Tabs>
        <telerik:RibbonBarTab Text="home">
            <%-- duplicate the group and items inside to replicate more easily --%>
            <telerik:RibbonBarGroup Text="Documents">
                <Items>
                    <telerik:RibbonBarButton Text="Item 1" />
                </Items>
            </telerik:RibbonBarGroup>
        </telerik:RibbonBarTab>
    </Tabs>
</telerik:RadRibbonBar>

Workaround: 

Telerik.Web.UI.RadToolBar.Views.Lite.prototype._repaint = function () {
    this._updateItemsTextAndImage();
    this._showAllHiddenItems();
    if (this._owner.get_orientation() == Telerik.Web.UI.Orientation.Horizontal) {
        this._responsiveCheck();
    }
}

I have a lot of exceptions "This is an invalid webresource request" on URL:
Url: 
http://localhost:28346/WebResource.axd?d=pA8zoJJ2yE9oO6Ia28y3ulqgm2EN3siWz944xQWIIGBXVpgk0BapHVTl4shvvFk6xNdt4LtiZSHEyXvbblVt01x0HwUwNQaOMxMWgBjtZYGpgc8UslSNdkbp6cUlZ40ejI7_lKB_ojLYUsqy5MqXRvXtaiUCAP9m7jUF4h8I34ewKZ8vyOpjWEbtWAuKDJ9m0&t=635173510100000000
I decoded content of url:
Telerik.Web.UI.Skins|Telerik.Web.UI.Skins.Web20.Common.radGradientListSprite.png
Probably there is no radGradientListSprite.png for Web20 skin inside dll file.
Could you check it?
Regards...

KeyboardNavigationSetting property Activated does not work, when set to True:
- JavaScript error thrown when KeyboardNavigationSetting Activated is set to true in Classic render mode.
- Nothing happens in Lightweight render mode.

For the time being you can use the ApplicationMenu withing the RadRibbonBar control.