Comment 7 for bug 848562

I have found a workaround: for some reason, the password dialog wants to only show up on one of the monitors, but only the one on which the mouse is when showing the password dialog is displaying "stuff" (stuff being anything else besides the top bar). So what I do when I don't see the password dialog is to press escape once, then move the mouse to the other monitor, and press escape again.

This may have something to do with the fact that I'm using nVidia drivers (there are always some annoyances with it and two-monitor setup). Nouveau had better behaviour with two monitors, but I have not been using it for a very long time.