How to stop TabItems moving around

Question

I have a TabControl with lots of TabItems creating 2 rows of tab items. When I click on a tab in the first row, the whole row moves to the second row position and the second row moves to the top. How do I stop these tabs from moving around?

Before clicking on a tabitem:

After clicking on the File tabitem:

Answer 1

Replace the TabPanel in the default ControlTemplate with a WrapPanel. You need to re-define the entire template:

<TabControl>
     <TabControl.Template>
        <ControlTemplate TargetType="{x:Type TabControl}">
            <Grid x:Name="templateRoot" ClipToBounds="true" SnapsToDevicePixels="true" KeyboardNavigation.TabNavigation="Local">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition x:Name="ColumnDefinition0"/>
                    <ColumnDefinition x:Name="ColumnDefinition1" Width="0"/>
                </Grid.ColumnDefinitions>
                <Grid.RowDefinitions>
                    <RowDefinition x:Name="RowDefinition0" Height="Auto"/>
                    <RowDefinition x:Name="RowDefinition1" Height="*"/>
                </Grid.RowDefinitions>
                <WrapPanel x:Name="headerPanel" Background="Transparent" Grid.Column="0" IsItemsHost="true" Margin="2,2,2,0" Grid.Row="0" KeyboardNavigation.TabIndex="1" Panel.ZIndex="1"/>
                <Border x:Name="contentPanel" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Grid.Column="0" KeyboardNavigation.DirectionalNavigation="Contained" Grid.Row="1" KeyboardNavigation.TabIndex="2" KeyboardNavigation.TabNavigation="Local">
                    <ContentPresenter x:Name="PART_SelectedContentHost" ContentSource="SelectedContent" Margin="{TemplateBinding Padding}" SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
                </Border>
            </Grid>
            <ControlTemplate.Triggers>
                <Trigger Property="TabStripPlacement" Value="Bottom">
                    <Setter Property="Grid.Row" TargetName="headerPanel" Value="1"/>
                    <Setter Property="Grid.Row" TargetName="contentPanel" Value="0"/>
                    <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                    <Setter Property="Height" TargetName="RowDefinition1" Value="Auto"/>
                    <Setter Property="Margin" TargetName="headerPanel" Value="2,0,2,2"/>
                </Trigger>
                <Trigger Property="TabStripPlacement" Value="Left">
                    <Setter Property="Grid.Row" TargetName="headerPanel" Value="0"/>
                    <Setter Property="Grid.Row" TargetName="contentPanel" Value="0"/>
                    <Setter Property="Grid.Column" TargetName="headerPanel" Value="0"/>
                    <Setter Property="Grid.Column" TargetName="contentPanel" Value="1"/>
                    <Setter Property="Width" TargetName="ColumnDefinition0" Value="Auto"/>
                    <Setter Property="Width" TargetName="ColumnDefinition1" Value="*"/>
                    <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                    <Setter Property="Height" TargetName="RowDefinition1" Value="0"/>
                    <Setter Property="Margin" TargetName="headerPanel" Value="2,2,0,2"/>
                </Trigger>
                <Trigger Property="TabStripPlacement" Value="Right">
                    <Setter Property="Grid.Row" TargetName="headerPanel" Value="0"/>
                    <Setter Property="Grid.Row" TargetName="contentPanel" Value="0"/>
                    <Setter Property="Grid.Column" TargetName="headerPanel" Value="1"/>
                    <Setter Property="Grid.Column" TargetName="contentPanel" Value="0"/>
                    <Setter Property="Width" TargetName="ColumnDefinition0" Value="*"/>
                    <Setter Property="Width" TargetName="ColumnDefinition1" Value="Auto"/>
                    <Setter Property="Height" TargetName="RowDefinition0" Value="*"/>
                    <Setter Property="Height" TargetName="RowDefinition1" Value="0"/>
                    <Setter Property="Margin" TargetName="headerPanel" Value="0,2,2,2"/>
                </Trigger>
                <Trigger Property="IsEnabled" Value="false">
                    <Setter Property="TextElement.Foreground" TargetName="templateRoot" Value="{DynamicResource {x:Static SystemColors.GrayTextBrushKey}}"/>
                </Trigger>
            </ControlTemplate.Triggers>
        </ControlTemplate>
    </TabControl.Template>
    ...
</TabControl>