Possible Bug: Template's TargetType property does not match its control type

Question

Hi

I'm working on a C++ Metro style app. I use a resource dictionary from which I define styles for several controls, for example a group of radio buttons. The designer shows an error ("Template's TargetType property does not match  its control type") but only for the first of these buttons. I can't figure out any mistake, maybe there is one, but since I am able to compile I may assume that this is a bug.

Simplified code for the controls inside my page:

<RadioButton x:Name="m_btnTone0" Content="1" Style="{StaticResource ToneButton}"/>
<RadioButton x:Name="m_btnTone1" Content="2" Style="{StaticResource ToneButton}"/>

Simplified code for the style inside the dictionary:

<Style x:Key="ToneButton" TargetType="RadioButton">
        <Setter Property="FontSize" Value="21.333"/>
        <Setter Property="FontWeight" Value="Bold"/>
        <Setter Property="VerticalContentAlignment" Value="Bottom"/>
        <Setter Property="HorizontalContentAlignment" Value="Left"/>
        <Setter Property="ClickMode" Value="Press"/>
        <Setter Property="GroupName" Value="ToneButtonsGroup"/>
    </Style>