I've been working on a case with Microsoft for the past year and we finally might have found the underlying issue. In trying to verify whether the issue was correctly identified Microsoft created a private fix for us.
To install this fix you have to jump through a few hoops but it is pretty straight forward.
And while getting your system out of the test mode is just as easy as getting it into test mode - removing the desktop watermark seems to be a different story. Until you know how to.
But lets begin at the top.