Here are a few options to avoid or recover from the issue.
In the main bug ticket there's now a fix which involves adding a PPA:
Add the Xubuntu Developers PPA to get the new packages:
sudo add-apt-repository ppa:xubuntu-dev/ppa
Update package information and update the two crucial packages:
sudo apt-get update && sudo apt-get install xfce4-power-manager light-locker-settings
xfce4-power-manager-data will get upgraded at the same time
Restart your machine.
To remove the upgrades and return your machine to it's state prior to testing
sudo ppa-purge ppa:xubuntu-dev/ppa
The easiest way to work around this bug is to disable lock on suspend in the light locker settings. Of course, this means that your machine will resume from suspend without a password.
If you end up in this situation you can get back to a working state (note that you'll lose your current session and a new one will be started) by:
Switch to a virtual terminal: CtrlAltF1
Restart lightdm: sudo service lightdm restart
This is a known Bug and has been reported, click here to see the source of the info