Triggered Blend animation on page's loaded event fired too early - xaml

Question

I'm having issues as I'm trying to start storyboard animation when application starts. I have fast storyboard animation (0.5 seconds), attached to main page's Loaded event via EventTriggerBehavior in Blend which starts storyboard animation. But almost every time application (after hiding splash screen) animation is already done.
Here is my XAML (for WP8.1; but same applies for 8.1 store application):
<Page
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:OnloadAnimation"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:Interactivity="using:Microsoft.Xaml.Interactivity" xmlns:Core="using:Microsoft.Xaml.Interactions.Core" xmlns:Media="using:Microsoft.Xaml.Interactions.Media"
x:Class="OnloadAnimation.MainPage"
mc:Ignorable="d">
<Page.Resources>
<Storyboard x:Name="OnloadStoryboard">
<DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(CompositeTransform.TranslateX)" Storyboard.TargetName="rectangle">
<EasingDoubleKeyFrame KeyTime="0" Value="0">
<EasingDoubleKeyFrame.EasingFunction>
<ExponentialEase EasingMode="EaseInOut" Exponent="5"/>
</EasingDoubleKeyFrame.EasingFunction>
</EasingDoubleKeyFrame>
<EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="367.164">
<EasingDoubleKeyFrame.EasingFunction>
<ExponentialEase EasingMode="EaseInOut" Exponent="5"/>
</EasingDoubleKeyFrame.EasingFunction>
</EasingDoubleKeyFrame>
</DoubleAnimationUsingKeyFrames>
<DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="(UIElement.RenderTransform).(CompositeTransform.TranslateY)" Storyboard.TargetName="rectangle">
<EasingDoubleKeyFrame KeyTime="0" Value="0">
<EasingDoubleKeyFrame.EasingFunction>
<ExponentialEase EasingMode="EaseInOut" Exponent="5"/>
</EasingDoubleKeyFrame.EasingFunction>
</EasingDoubleKeyFrame>
<EasingDoubleKeyFrame KeyTime="0:0:0.5" Value="400">
<EasingDoubleKeyFrame.EasingFunction>
<ExponentialEase EasingMode="EaseInOut" Exponent="5"/>
</EasingDoubleKeyFrame.EasingFunction>
</EasingDoubleKeyFrame>
</DoubleAnimationUsingKeyFrames>
</Storyboard>
</Page.Resources>
<Interactivity:Interaction.Behaviors>
<Core:EventTriggerBehavior EventName="Loaded">
<Media:ControlStoryboardAction Storyboard="{StaticResource OnloadStoryboard}"/>
</Core:EventTriggerBehavior>
</Interactivity:Interaction.Behaviors>
<Grid Background="#FF1D1D1D">
<Rectangle x:Name="rectangle" Fill="#FFF4F4F5" HorizontalAlignment="Left" Height="205" Stroke="Black" VerticalAlignment="Top" Width="200" RenderTransformOrigin="0.5,0.5">
<Interactivity:Interaction.Behaviors>
<Core:EventTriggerBehavior EventName="PointerPressed">
<Media:ControlStoryboardAction Storyboard="{StaticResource OnloadStoryboard}"/>
</Core:EventTriggerBehavior>
</Interactivity:Interaction.Behaviors>
<Rectangle.RenderTransform>
<CompositeTransform/>
</Rectangle.RenderTransform>
</Rectangle>
</Grid>
</Page>
Also here is full solution.