Question

Apologies if the answer to this question is completely obvious but it has me stumped at the moment. Why will the textboxes in this example not receive focus? If I use vanilla textboxes without the control template the focus works fine.

<StackPanel>
        <Label Name="lblChartTitle"
            Content="{x:Static res:Strings.ChartOptionsTitlesControlView_Label_Title}" />
            <TextBox Name="txtChartTitle" 
                     Text="{Binding Path=ChartTitle}" 
                     MaxLength="255"
                     KeyboardNavigation.TabIndex="1"
                     Template="{DynamicResource ctTextBox3DInset}"
                     />
        <Label Name="lblChartCategoryXAxis"
            Content="{x:Static res:Strings.ChartOptionsTitlesControlView_Label_CategoryXAxis}" />
            <TextBox Name="txtChartCategoryXAxis" 
                     Text="{Binding Path=CategoryXAxis}" 
                     MaxLength="255" 
                     KeyboardNavigation.TabIndex="2"
                     Template="{DynamicResource ctTextBox3DInset}"
                     />
        <Label Name="lblChartValueYAxis"
            Content="{x:Static res:Strings.ChartOptionsTitlesControlView_Label_ValueYAxis}" />
            <TextBox Name="txtChartValueYAxis" 
                     Text="{Binding Path=ValueYAxis}" 
                     MaxLength="255"
                     KeyboardNavigation.TabIndex="3"
                     Template="{DynamicResource ctTextBox3DInset}"
                     />
    </StackPanel>

<ControlTemplate x:Key="ctTextBox3DInset" TargetType="TextBox">
            <Border 
                Style="{StaticResource BorderStyle3DInsetBlack}"
                Margin="0,0,0,5">
                <Border Style="{StaticResource BorderStyle3DInsetWhite}">
                    <Border Style="{StaticResource BorderStyle3DInset}">
                        <TextBox
                            TabIndex="{TemplateBinding TabIndex}"
                            BorderThickness="0"/>
                    </Border>
                </Border>
            </Border>
        </ControlTemplate>

Answer 1

Because when you apply the ControlTemplate, you are actually creates another TextBox.. So the focus is not set to the TextBox within your ControlTemplate.

Edit:

What you need to use is actually <ContentPresenter/>:

<ContentPresenter/>

instead of creating a TextBox using

<TextBox  TabIndex="{TemplateBinding TabIndex}" 
                        BorderThickness="0"/> 

Edit 2: I think my previous answer was wrong, TextBox work differently.
You have to use <ScrollViewer Margin="0" x:Name="PART_ContentHost"/> for TextBox, PART_ContentHost is a special name for assign an element as content host. And must be use with ScrollViewer or an AdornerDecorator.

Here is the reference