Windows10 on two monitors, at least one of them is with higher DPI -125 , 150 %. This leads to unexpected black gap (glitch) between the RibbonWindow TitleBar and Content. Partial workaround is to set manually a margin on the WindowDecorator: private void RadRibbonWindow_Loaded(object sender, RoutedEventArgs e) { Grid windowDecorator = this.ChildrenOfType<Grid>().FirstOrDefault(x => x.Name == "MaximizedWindowDecorator"); windowDecorator.Margin = new Thickness(0, -1, 0, 0); }