UserControl animation doesn't apply after binding content - wpf

Question

Please don't get daunted by the size of the code. It is a very small user control.
This user control is supposed to wave the text inside it (marquee) :
<UserControl x:Class="WpfTest.Marquee"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="clr-namespace:WpfTest"
mc:Ignorable="d"
d:DesignHeight="25" d:DesignWidth="50">
<UserControl.Resources>
<Storyboard x:Key="Storyboard1" AutoReverse="True" RepeatBehavior="Forever">
<DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(TransformGroup.Children)[3].(TranslateTransform.X)" Storyboard.TargetName="label">
<EasingDoubleKeyFrame KeyTime="0:0:0" Value="0"/>
<EasingDoubleKeyFrame KeyTime="0:0:2" Value="-100"/>
</DoubleAnimationUsingKeyFrames>
</Storyboard>
</UserControl.Resources>
<UserControl.Triggers>
<EventTrigger RoutedEvent="FrameworkElement.Loaded">
<BeginStoryboard Storyboard="{StaticResource Storyboard1}"/>
</EventTrigger>
</UserControl.Triggers>
<Grid Width="50">
<StackPanel Width="1000">
<Label x:Name="label"
Content="{Binding Content, FallbackValue='a long long text to test'}"
RenderTransformOrigin="0.5,0.5" ClipToBounds="False"
>
<Label.RenderTransform>
<TransformGroup>
<ScaleTransform/>
<SkewTransform/>
<RotateTransform/>
<TranslateTransform X="-20" />
</TransformGroup>
</Label.RenderTransform>
</Label>
</StackPanel>
</Grid>
</UserControl>
When I use it without changing the content it works fine and animation works:
<Window x:Class="WpfTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfTest"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<local:Marquee></local:Marquee>
</Grid>
</Window>
But when I assign content to it the animation doesn't apply :
<Window x:Class="WpfTest.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:WpfTest"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<local:Marquee Content="This is another long long text to test"></local:Marquee>
</Grid>
</Window>
Do you know how can I make it working after binding the content?