I can confirm this behavior. It seems to be somehow related to either the windows button or search button on the taskbar. At least it seems to appear after I have interacted with one or the other. Restarting the computer gets rid of it of course but that is rather annoying.
Btw, a workaround that works for me is to turn off transparency effects in the settings. You still have to log out and in again for that to take effect but after that it seems to have stopped on my computer.