Created attachment 52915 [details] screenshot Version: 4.5 OS: Linux Not always, but often, when I login there is a rectangle made just by shadow (as the shadow of a window, black colour) on top-left of my screen. To make it disappear I have to turn off compositing and then turn it on. During this two moves, for just a moment this rectangle becomes fully black. This happens also with another user on the same machine. Reproducible: Sometimes Steps to Reproduce: Just log in. Actual Results: turning off and on the compositing removes it until next login.
*** This bug has been marked as a duplicate of bug 251537 ***