Steps to reproduce:

1. Open attached project "835218.zip" and deploy to UWP
2. Open built solution using VS and run on Local Machine
3. Once build starts notice "+++++Created" in console. This means that there wasn't PlayerPref under the key so one was created
4. Close build and start one again using start menu. It should be listed as "Test_PlayerPrefs"
5. Notice message "+++++Created" - this means that there was't PlayerPref under the key (= PlayerPref created in last run wasn't saved)

Reproducible on Universal 8.1/10.

Reproduced with: 5.4.1p3, 5.5.0b6
Not reproducible: 5.4.1f1