unity-greeter sometimes does not start properly

[Bradford Hovinen]

At times the Unity greeter does not display. I see only a black screen with a mouse-cursor. To workaround, I must switch to VT1, log in with getty, and kill the process unity-greeter. It then restarts properly. The bug has only occurred in the last three weeks and occurs completely at random, perhaps once every three times I boot.

Neither dmesg nor /var/log/syslog have any relevant entries.

I am running Ubuntu 12.04 LTS on x86-64 and all packages are up to date.

I cannot say whether the problem started immediately after a recent software-update. It was not however precipitated by any software-installation or change in configuration.