I too suffer from invisible unlock screen, but I have a Radeon card, not Nvidia. I do use dual-head layouts (MergedFB) also, but the unlock screen appears invisible even in single-head mode. I can type in my password blindly and unlock the session.
This seems to only happen when I use the 'blank screen' screensaver. -- Unlock screen is invisible with Nvidia twinview https://launchpad.net/bugs/45018 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
