Storyboard animation only displays last frame - animation

Question

I have to create an animation for a Windows Phone 8.1 app. I want to change the ImageSource property of my Page.Background to display an animated splash when the app launches.
I used this sample as a model: http://www.codeproject.com/Tips/823622/Images-Animation-By-Using-Story-Board-in-Windows-P
In my code, the animation lasts 8 seconds for 80 images, but the screen stays black for 8 seconds, then only displays the last frame.
private void setupStoryboard()
{
storyboard = new Storyboard();
var animation = new ObjectAnimationUsingKeyFrames();
Storyboard.SetTarget(animation, BackgroundBrush);
Storyboard.SetTargetProperty(animation, "ImageSource");
storyboard.Children.Add(animation);
for (int i = 0; i <= 80; i++)
{
var keyframe = new DiscreteObjectKeyFrame
{
KeyTime = KeyTime.FromTimeSpan(TimeSpan.FromMilliseconds(100 * i)), //Time Interval
Value = String.Format("ms-appx:///Assets/Animation/splash{0:D2}.png", i) //Source of images
};
animation.KeyFrames.Add(keyframe);
}
Resources.Add("Storyboard", storyboard); //Add story board to resources
}
This code is called from OnNavigatedTo, and I have a button to call storyboard.Begin();
This problem appears on simulator and device.
Update: The problem persists with a greater interval (1000ms), and smaller images (30KB jpg instead of 240KB png)
Update: Same problem with an <Image> tag
Update: Still not solved, but I managed to obtain the desired effect. I created a DispatcherTimer to manually change the image. Unfortunately, this creates a nasty flickering effect. I had to add a second identical image on top of the first, and alternate between the two: imageA loads source1, imageB loads source2, imageA loads source3, ImageB loads source4...
Mission completed, with duct tape.