To rperoduce:
- Set the themes as follows:
var theme = new Office2010BlackTheme();
new Telerik.WinControls.RadControlSpy.RadControlSpyForm().Show();
ThemeResolutionService.ApplicationThemeName = theme.ThemeName;

this.radRibbonBar1.ElementTree.EnableApplicationThemeName = false;
this.radRibbonBar1.ThemeName = "ControlDefault";

- Start and collapse the ribbon tabs. 
- Click on a tab to show its controls.

Workaround: Use the ApplyThemeToControlTree method instead of settig the ApplicationThemeName property.
ThemeResolutionService.ApplyThemeToControlTree(this, "Windows");