Comment 5 for bug 990887

This issue appears not just at the lightdm login screen but also if you are in a virtual terminal.

For a work around try the recommendation on this site:
http://www.infty.nl/wordpress/2012/12/gnome-3-on-ubuntu-raring-and-suspend/comment-page-1/

Similar instructions are here but without the explanation:
http://askubuntu.com/questions/71033/closing-the-lid-isnt-toggeling-standby-anymore-after-update-in-lubuntu-how-can

I named the created file lid.sh.pre not lid.sh.post as /etc/acpi/lid.sh already references lid.sh.post. Don't forget to make the file executable (like I usually do) as instruscted on that page.