Comment 9 for bug 471457

Just made a clean install of Ubuntu saucy and this started happening to me sometimes.

I believe the issue happens due to systemd-logind, which is set to always standby a laptop when you close the lid, and the supposed solution can be found here: http://askubuntu.com/questions/360615/ubuntu-server-13-10-now-goes-to-sleep-when-closing-laptop-lid (the HandleLidSwitch=ignore option).

Because this doesn't happen always I can't be 100% sure; I'm running with that option set for a few days, and if the issue never happens to me again I'll report this as a systemd-logind bug.