I am also having this issue. I attempted the "unity --replace" workaround, and it appeared to kill my existing session.
I'd also like to note that I use VMWare workstation (my machine with the problem is the host) and if I leave my cursor in my vmware window the screensaver doesn't activate until I move my mouse out of VMware. This may be unreleated but I wanted to mention it in case it is meaningful to others. HP EliteBook 8770w, Ubuntu 14.04.1 64bit, Nvidia Proprietary drivers: 331.38. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to unity in Ubuntu. https://bugs.launchpad.net/bugs/1311316 Title: After locking screen there is no input field to type password for unlock Status in Unity: Triaged Status in “unity” package in Ubuntu: Confirmed Bug description: Sometimes (but not always) after locking the screen there is the situation not having any input field where I can type the password to unlock the session again. The shaded gray area simply does not have the input field. I can't do anything, I have to switch to text console and stop/start lightdm service to cure the problem loosing all of my session :( ProblemType: Bug DistroRelease: Ubuntu 14.04 Package: unity 7.2.0+14.04.20140416-0ubuntu1 ProcVersionSignature: Ubuntu 3.13.0-24.46-generic 3.13.9 Uname: Linux 3.13.0-24-generic i686 ApportVersion: 2.14.1-0ubuntu3 Architecture: i386 CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins' CurrentDesktop: Unity Date: Tue Apr 22 22:17:57 2014 InstallationDate: Installed on 2012-03-03 (780 days ago) InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1) SourcePackage: unity UpgradeStatus: Upgraded to trusty on 2013-10-18 (186 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/unity/+bug/1311316/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp