I'm trying to get a UserControl to tab properly and am baffled. The logical tree looks like this.

|-Window
  -Grid
    -TabControl
      -TabItem
        -StackPanel
          -MyUserControl
            |-StackPanel
              -GroupBox
                -Grid
                  -ComboBox
                    -Textbox1
                      -Textbox2

Everything works fine, except when the visibility converter for the ComboBox returns Visibility.Collapsed (don't allow user to change database mode), then when textbox1 is selected, instead of being able to tab through the controls in the UserControl, the focus shifts to a button declared at the bottom of the window. Nothing else apart from the controls displayed has TabIndex or FocusManager properties set.

I'm banging my head against a brick wall and I must be missing something. I've tried IsFocusScope=True/False, played with FocusedElement and nothing works if that ComboBox is invisible (Visibility.Collapsed).

<Window x:Class="MyNamespace.Client.WinInstaller"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    FocusManager.FocusedElement="{Binding ElementName=tabWizard}">
    <Window.Resources>
        <props:Settings x:Key="settings" />
    </Window.Resources>
    <Grid Grid.IsSharedSizeScope="True">
        <!-- row and column definitions omitted -->

        <loc:SmallHeader Grid.Row="0" x:Name="headerBranding" HeaderText="Setup" />
        <TabControl x:Name="tabWizard" DataContext="{StaticResource settings}" SelectedIndex="0" FocusManager.IsFocusScope="True">
            <TabItem x:Name="tbStart" Height="0">
                <StackPanel>
                    <TextBlock Text="Database Mode"/>
                    <loc:DatabaseSelector x:Name="dbSelector" AllowChangeMode="False" TabIndex="1"
                                          AvailableDatabaseModes="SQLServer" IsPortRequired="False"
                                          DatabaseMode="{Binding Default.DbMode,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                                          DatabasePath="{Binding Default.DatabasePath,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"/>
                </StackPanel>
            </TabItem>
        ...

The top of the user control is below:

<UserControl x:Class="MyNamespace.Client.DatabaseSelector"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Name="root"
    FocusManager.IsFocusScope="True"
    FocusManager.FocusedElement="{Binding ElementName=cboDbMode}">
    <UserControl.Resources>
        <conv:DatabaseModeIsFileBased x:Key="DatabaseModeIsFileBased"/>
        <BooleanToVisibilityConverter x:Key="BooleanToVisibilityConverter"/>
    </UserControl.Resources>
    <StackPanel DataContext="{Binding}">
        <GroupBox>
            <Grid>
                <!-- row and column definitions omitted -->
                <Label Content="Database Mode"/>
                <ComboBox x:Name="cboDbMode" SelectedValue="{Binding ElementName=root,Path=DatabaseMode,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                          DisplayMemberPath="Value" SelectedValuePath="Key" TabIndex="1" Visibility="{Binding AllowChangeMode,ElementName=root,Converter={StaticResource BooleanToVisibilityConverter}}" />
                   <!-- AllowChangeMode is a DependencyProperty on the UserControl -->
                <Grid><!-- row and column definitions omitted -->
                    <Label "Host"/>
                    <TextBox x:Name="txtDBHost" Text="{Binding ElementName=root,Path=DatabaseHost,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" TabIndex="2" />
                    <TextBox x:Name="txtDBPort" Text="{Binding ElementName=root,Path=DatabasePortString,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}" TabIndex="3" />