If I use your RadTabControl, I get error 26 in the Output window. Why?
System.Windows.Data Error: 26 : ItemTemplate and ItemTemplateSelector are ignored for items already of the ItemsControl's container type; Type='RadTabItem'
<telerik:RadTabControl x:Name="tabControl" Grid.Row="1" VerticalAlignment="Top"
DisplayMemberPath="Content" DropDownDisplayMode="Visible" ScrollMode="Viewport">
<telerik:RadTabItem />
</telerik:RadTabControl>
I copied the Windows 7 theme from \RadControls for WPF Q3 2012\Themes.Implicit\WPF40\Windows7\Themes:
<Window.Resources>
<ResourceDictionary>
<ResourceDictionary.MergedDictionaries>
<ResourceDictionary Source="../Themes/Telerik.Windows.Controls.Navigation.xaml"/>