Unexpected style changes in WPF

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C#

WPF

style

trigger

I have a TabControl that has a frame in each TabItem. I only listed one TabItem below for simplicity. Whenever I move my mouse over any control in the frame, the IsMouseOver style change occurs on the selected TabItem in the TabControl and changes to Gray. What am I doing wrong?

Update: I seperated the ControlTemplate from the style and set the template of the button to use the ControlTemplate and no styling. It seems to be a problem with the ControlTemplate, because it still happens.

<TabControl Margin="10" BorderThickness="0" TabStripPlacement="Left" SnapsToDevicePixels="True" >
         <TabItem Header="General"  Style="{DynamicResource TopItem}"  Tag="Top" >

             <Frame NavigationUIVisibility="Hidden"   Source="Settings.xaml" />

         </TabItem>

     </TabControl>

<Style TargetType="TabItem"  x:Key="TopItem">
        <Style.Triggers>
            <Trigger Property="IsSelected" Value="True">

                <Setter Property="Foreground" Value="White" />
            </Trigger>
        </Style.Triggers>
        <Setter Property="Background" Value="Transparent"/>
        <Setter Property="FontFamily" Value="Georgia"/>
        <Setter Property="FontSize" Value="14"/>

        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type TabItem}">
                    <Grid x:Name="Panel" >
                        <Border x:Name="ItemBorder" BorderThickness="1,0,1,0"     BorderBrush="Black"  Padding="10" Width="150">

                            <ContentPresenter x:Name="ContentSite"
        							VerticalAlignment="Center"
        							HorizontalAlignment="Center"
        							ContentSource="Header"
        							/>
                        </Border>

                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="Tag" Value="Top">
                            <Setter TargetName="ItemBorder" Property="BorderThickness" Value="1,1,1,0" />
                            <!--<Setter TargetName="ItemBorder" Property="CornerRadius" Value="5,5,0,0" />-->

                        </Trigger>
                        <Trigger Property="Tag" Value="Bottom">
                            <Setter TargetName="ItemBorder" Property="BorderThickness" Value="1,0,1,1" />
                            <!--<Setter TargetName="ItemBorder" Property="CornerRadius" Value="0,0,5,5" />-->

                        </Trigger>
                        <Trigger Property="IsSelected" Value="True">
                            <Setter TargetName="ItemBorder" Property="Background" Value="#FF124E8D" />
                        </Trigger>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter TargetName="ItemBorder" Property="Background" Value="Gray" />
                        </Trigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>