I think the easiest way to reproduce the problem is like this (REMEMBER this will most likely hang your computer requiering a forced restart, I don't take any responsibiblity for any trouble that might cause you):
1. Have the MacBook Air (Mid 2013) running with the display/lid open.
2. Hold down the ”cmd alt/option” keys and press the power key (this will cause the MacBook Air to enter sleep mode)…
3. …then immediately after pressing the above key combo, press random keys on the keyboard in an attempt to wake up the computer.
After the first or a few tries you should have a hanged MacBook Air, i.e. black screen and not responding to keyboard input.
I've noticed that it sometimes doesn't hang directly (still responding to keyboard input) but the screen stays black. After a while it seems it hangs, though. Can be that it restarts automatically (”because of a problem”) that you then can send to Apple.
Anyway, like has been said before, though: it seems Apple are aware of this and a Firmware fix will hopefully come out relatively soon to take care of it.