New
#11
The test build watermark suggests to me its a beta or pre beta version. Those versions have a time limit on them and expire. Microsoft doesn't want you using them past a certain point and want you to buy an official retail version. If you research it you'll likely find one of the things that happens after the time runs out is you loose your wallpaper. Forced reboots after a couple of hours was another gotcha I think. I think there was a thread on this at one point, might even be a sticky.
EDIT: ops, test mode isn't the same thing as test build so I may be off track.