The designer crashes with this exception: InvalidOperationException: 'GridViewColumnGroupRow' TargetType does not match type of element 'GridViewColumnGroupRow'. See the attached screenshot. It's from a new project, after clean and rebuild. Visual studio: 2015 Telerik UI for wpf: 2015.2 Implicit styles, Windows8 theme. * The problem is not theme specific. As a workaround, use no xaml binaries instead of xaml files.