Reproduction steps:
1. Open the attached project and build it to WSA (SDK 10 or 8.1)
2. Deploy the project to MS Surface Pro (it has built in speakers)
3. Press Mouse2 (or press two fingers on the screen) to download an mp3 file
4. When it's downloaded press "Play"
5. While the sound is playing plug in headphone
Result: The sound is played through speakers instead of headphones

- Not reproducible on Windows Phones
- Not reproducible in other Applications (tried Google Chrome with youtube playback)
- Sound is played through headphones if they're connected from the beginning (before opening player)

Reproduced with: 5.2.5f1, 5.4.1p3, 5.5.0b6