Workaround: change the backcolors of the splitters at run-time

foreach (SplitterElement splitter in this.radSplitContainer1.Splitters)
{
    splitter.BackgroundFill.BackColor = Color.Red;
}

To reproduce:
Set the DescriptionFont of RadMenuItem in VSB (see attached image).

Workaround: 
 Remove the setting from the XML.