I've also reported critical bug 12430, somewhere they may be the same.
What happened:
1. I have notebook with VGA port and DISPLAY.
2. I've used arandr to configure connected projector (exactly arandr due to 12424)
3. Then I turned off prjector and set one of notebooks displays to off in xfce4-display-conf. Noteboks displayed worked fine (i've suspended twice) till hibernation. After I've waked up I had black screen. Everything worked. I've set display to on blindly in arandr.

I can't remember which display I've disabled, cause they had dummy names.

The behavior is similar to 12430. So I suggest to poll the number of active displays. And if there is ZERO active display and More than ONE availible - turn on ONE of availible displays in list.