First I changed the theme to aero basic; it did not appear. When I ran net stop uxsms, then it appeared. I noticed in Visual Studio as well, that after running a build, part of the code editor (where the text is) is shifted around about in the same shape and area as the box, which appears in the top left corner, and sometimes appears to change shape...
I wonder if anyone else ever saw this phenomenon. Also, I think this happened a few driver updates ago.