Comment 12 for bug 1005545

Still seems to be affecting Mint 14 32-bit. Same symptoms as original poster and same "workaround"...moving mouse to secondary display and hitting escape loads lockscreen on secondary display, moving mouse back to primary display and hitting escape does not load lockscreen, loads that same black box. Easier to reproduce if you set your screen timeout/system lock to 1 minute of activity. Issue does not occur when computer is locked and monitors do not go into power save mode...if it is locked manually you can see the lock screen just fine.

My displays were set to different resolutions...when this was the case, I could see the bottom of the desktop background on the primary display and the time/user name at the top, but that was all. The blacked out area appeared to be the size of the resolution of the secondary display relative to the resolution of the primary display. When I changed the primary display to match the resolution of the secondary display, the blacked out area covered the entire area where the desktop picture would be and the only thing that was visible was the time and name at the top of the screen. It did not resolve the issue, though...hitting escape on the primary screen while the mouse is on the primary screen did not work, however hitting escape while the mouse is on the secondary screen brings up the lockscreen on the secondary screen without fail.

I switched displays and made the right display the primary one in nvidia config and let the computer lock itself and turn off the displays. The right display (now the primary) had the time and user name on top, but did not come up with the lock screen automatically. When I moved the mouse to the left display (now the secondary) and hit escape, the lock screen did not come up. When I moved the mouse to the right display and hit escape, the lock screen did come up and I was able to log in.

I flipped the position of the displays so that the one on the left physically was on the right logically (have to move mouse to left edge of left screen to get to right edge of right screen) and the screen logically on the right was consistently the one that was able to load the lock screen after moving the mouse to that screen and hitting escape.

I kept the same logical configuration but instead of using absolute coordinates I used the option in nvidia config that said "left of" to make the physically left monitor be logically to the right, and lo and behold, the lock screen appeared on the left (still non-primary x display) monitor. I then used the "right of" setting to make the right monitor actually on the right and the lock screen did not appear properly on either screen until the escape key was hit. I switched back to the setting that "worked" and it did not work the second time I tried it, but did the third.

Ultimately I figured out that it seems that the lock screen is defaulting to the right-most screen as defined in nvidia config, and if the mouse is left on that screen when the timer expires, it loads properly, but if the mouse is on the left-hand screen, the lock screen does not load until you move the mouse to the right-hand screen and hit escape. It does not appear that defining either of the displays as the primary display in nvidia config has any bearing on this issue whatsoever as the lock screen is still always on the right screen no matter which is the primary, and will only appear if the mouse is left on the right-most screen.