Comment 34 for bug 931967

This 1st occurred with the upgrade of unity-greeter to unity-greeter 0.2.1-0ubuntu1 though I believe the issue has been identified as being in lightdm

Unfortunately it's not that straightforward to test reverting back to that version due to dep changes with g-s-d, ect.

(if one was to install the gtk-greeter, switch to it for 1 restart, then switch back to the unity-greeter the 'corruption' will usually go away for a restart or 2, then start creeping back in